It all boils down to the gambler and the amount that he is aiming to win. If you play a single bet with little amount of money, you get little profits but parlay can give you a chance to increase that profits that you were to get from a single bet.

Also in parlay, you have the option to cashout when your bets are going as predicted, which means that you have nothing to lose by cashing out. If you don't cashout and the game turned out against you, that's the biggest regret. I have stopped betting on parlay, because it doesn't give me a rest of mind since I have to monitor the matches that I bet on.