All post positions are not equal when it comes to a horse's chances of winning a race. If you check the post position statistics for any track that you are planning to bet on, you'll find that some posts have an advantage over the others. So if a horse raced from a disadvantageous post in its last race and moves to a favorable one, how will it help?
If you are trying to pick horse racing winners there is a way to see if that change in post position will be enough to score a win. You'll have to do some research and spend some time creating a list of horses, but it will be worthwhile if your goal is to make money betting on the horses.
Here is what you do, first of all, get the stats and see which post(s) are the worst and which are the best. If post position 1 has a win average of 12% and post position 7 has a win average of 6%, it appears that post 1 is twice as good as post 7. Now here is the disclaimer, there may be many factors why a horse won or loss from that post and it doesn't mean that one post is twice as good as another. Another consideration is how many races are you using to arrive at those percentages? The more races the more reliable the study, right?
Well, maybe, it is more reliable and maybe not. While it is a good thing to have more races to be sure of accuracy and overcoming any anomalies, if the statistics include different seasons and periods of wet tracks and off tracks or sealed tracks, then it may not reflect the true condition of today's track or the post position bias. Try to use races that were run in the same season and weather conditions as today's race.
Do some research and find as many cases of horses who raced from the worst post and then moved to the better post and note the times of each race. You should see a pattern of improvement in the speed figures for each horse when it raced from the better post position. This is a very general study and doesn't take into account all the other variables, but it may show some kind of pattern and give you an idea of how much that one factor will improve a horse's performance.
Now, the next step is to find horses going from the good to the bad post or from the bad to the good post. Either situation will result in a change in final times and speed figures and you can factor that into your handicapping. So if you see a horse that can win at the level of today's race with a speed of 88 (the par speed figure for that distance and class) and you think the difference in post will help it to achieve that speed rating, then you have a winner, maybe.
Just remember that there are many variables that can affect a horse's performance and try to factor in as many as you can and finally, bet with your head and not over it. Enjoy your days at the races.