One of the fundamental axioms of sports betting at a professional level is that getting the better of the number; that is, placing your wagers at a better number than the number at close, is key to long-term success. Among other places, Pinnacle Sports has published a number of articles on this and there are several decent forum posts (this is the best and is also part of the very good book "Sharper" by pokerjoe) on the subject as well.
As a professional bettor I follow line moves very carefully; in fact, most of the time, I pay far more attention to line moves than the actual result of the game. This is because in my experience being on the right side of the line moves is far more predictive of future success than actual results.
Most professionals play in the morning as soon as their selection of outs allows max limits (in some cases they will play overnight instead, because many pay-per-head style bookies have the same limits overnight as during the day). Betting early on, in US major sports, if you are not consistently getting the better of the number around two-thirds of the time, you have almost no chance of winning. Something like getting favorable moves 55-60% of the time indicates that you are somewhat sharp and will likely be around break-even; you have some idea what you are doing but will be making too many bad wagers to really overcome the vig. Below that you will simply lose to the vig. Particularly if my recent results had not been good, not reaching the two-thirds benchmark would be a good reason to stop betting and re-evaluate my methods, and even if I have been winning, line moves against me would be a reason for further research.
Obviously the extra point or half point or 10 cents or whatever it is from getting a good line is important. In a game where big winners might average 5%, 10 cents is your entire winrate. But the more important reason why getting the better of the number is important has to do with the fundamental reason why lines move. In general, that reason is that winning players, who almost always bet whatever the limit is at as many books as they can, are betting that side of the game. Since by definition, these players win, any side other than what they are on probably loses, and by more than whatever the line moved. Winning players only bet when they have a decent edge on a game, and being on the wrong side means you not only pay the vig, but also that edge.
I think what is underestimated is how sharp these winning players are. The thing about sports betting is, if someone has a strong model and methodology, they generally keep winning. Eventually the market and other players will catch on, but this tends to take a while, and remember that someone smart enough to win in the first place is probably able to improve as well. As a result, for nearly every major sport you can think of, there are seven and often eight-figure lifetime winners. Some are in the news, but a lot of them are people no one has ever heard of.
At this highest level, most of these players don't even really bet at books like Pinnacle or Bookmaker, because the $10-30k they can bet at these books isn't worth their time (really) plus they don't want to tip these books off on which teams they like because it will hurt their prices on future games. But the books that they do bet at, who are often networks of local bookies or Asian bookies, tend to figure out where the action is coming from relatively quickly, and may well indeed bet these plays at major offshore books, and this will move the line. You just don't want to fade this action ever unless you have a very good reason to suspect it is dumb money or line manipulation.
I have read posts suggesting that one's winrate will be equal to whatever line value they get vs. the no-vig closing line at major sportsbooks. I disagree. In my experience, if your model is strong to the point that you almost always get the better of the move - and when you don't it's nearly always due to an injury or late news - you will win more than the line value you get. How much more depends on the sharpness of the market in question.
The other thing I see often is questions about why steam moves lose, and how it must be that no one is sharp anymore, Vegas has figured it out, etc. Most of the time this is just people who don't understand variance. However, it is true that some seasons, steam moves really do lose and more than just can be explained by variance alone. The 2016 NFL season was an example of this. Sharp plays absolutely got destroyed that season, with books having a terrible year as the public teams all covered.
The reason this happened is that in the NFL, most models in the past consistenly favored underdog teams, or at least teams that have played relatively poorly in recent games. Reversion to the mean is very powerful in the NFL; teams are so evenly matched that even teams who appear to be playing badly, based on the most predictive underlying stats and not just raw results, are still often just suffering negative variance. Models also tend to favor reversion to the mean in totals as well. But in 2016, there were a few teams that legitimately were terrible, and the models picked these teams week after week. The Cleveland Browns were particularly notable; most models would consistenly pick them week after week with the assumption that they couldn't be as bad as the stats indicated. Of course, unlikely most NFL teams in the past, the Browns were tanking, and really were that bad, and a few other teams probably starting taking the "Moneyball" or "Process" view as well, which wouldn't have happened several years ago.
Just like what happened in 2016 in the NFL, the most common reason for a bloodbath among sharps is a fundamental change in the sport in question, such that handicapping approaches based on certain statistics, trends, or other information, which were effective in the past, no longer predict future games as well. What tends to happen at the highest levels of sports betting is that those who move the numbers all like the same plays, as often they are using statistical models and approaches that are relatively similar. In other words, the "gene pool" of winning sports bettors is more shallow than it seems. When a sport changes, which can be due to rule and equipment changes (see MLB in late 2015-2016), changes in coaching or organizational philosophy, and even darker aspects like fixing, these players will often all lose at once.
Just like in real life though, evolutionary forces will sharpen the market. For one, some of these winners will evolve and figure things out quicker than others. Some may even have an approach so sophisticated that they were able to take advantage of the changes in the sport. These winners will keep winning. Second, often when one type of handicapping approach fails (and by approach I usually mean specific statistical modeling techniques and information), others will become better predictors. Those who use these predictors will win money and wager more in future seasons, and contribute to market moves. These factors will re-balance the market in future seasons. As such, in the long run getting the better of the number has to win, unless sportsbooks become incredibly stupid (which has certainly happened before).
The question you should ask yourself when a play moves against you is, why did this play move against me? There are two reasons - one is that you were on the wrong side to begin with, and did not handicap the game well. The other is, you may have been on the right side, but new information such as injury/weather announcements came out following your bet meaning you are now wrong. A quick check of related news will confirm this. There is a third possibility, that public action moved the line, but that is usually pretty rare.
The solution to the first issue with line moves is pretty simple - work on your model and probably quit betting in the meantime. A corrolary is, if you see a line move on a side you didn't like enough to bet before, but now you would like to make the bet - fading the line move - you should probably pass on that game.
The second issue of line moves going against the player due to injuries is a major challenge to the winning player. While the books put up opening numbers often without any advance knowledge of injuries, a lot of times there will be a few folks with insider knowledge of key injury news. If no such insider info existed, you would find that you would benefit from these types of moves as often as they hurt you. In reality, this doesn't happen. Lines will slowly drift early on for what seems like no good reason, making one side seem the value play, when in reality the reason for this movement is that those in the know are accumulating a position. No matter what, if you bet before lineups and injuries are fully announced and you don't have insider knowledge, you are going to take slightly the worst of it on these announcements. But in general if you have a winning methodology, and keep good track of injuries, you are still better off betting early before the lines have moved.
The challenge with sports betting is that short term variance makes it difficult to determine the validity of one's handicapping approach. Closing line value is a great yardstick with less variance than game by game results. While it is no guarantee of a high win rate, especially in small sports, in major sports, getting good lines versus the close almost certainly will in the long run.