Your return for a win is effectively your stake (minus commission). A lot of people prefer to lay at odds-on as your liability is then reduced. For example, if you lay a bet at 1.50 for 10 you are liable for 5 and will win 10 if the bet wins.
With lay betting, you are betting on any other possibility. For example, if you place a lay bet on Team A, you will make a profit if Team A loses or the game ends in a draw.