This allows you to have an edge over the bookmakers. There are a few things you can do to find value bets. First is to get into smaller leagues.
Getting into a small leagues doesn't really give you an advantage or an edge over the bookmakers cause in most cases you get uncertainties and most likely there would be more records of mistakes that can't be reversed so how do one achieve that. So I don't see the reason for it been called a value bets when there are always probabilities.
With what I have noticed about bookies, they really know how to make the odds perfect to how they will make money from people. Going for small leagues that you do not understand may even lead to more losses than going for big leagues that you understand. People only talk about valued bets, but it is not what it seems in reality.