The advantages of a parlay bet are the increased odds of the bet. With March Madness odds in particular, especially in the early rounds of the bracket, you will have overwhelming favorites with odds that can be a very short price and unappealing to bettors.
Parlay bets offer a great way around that by combining the selections to provide a much larger return.
For example, if you wanted to place a bet on Kentucky, Kansas, and Gonzaga all to win their matches and assuming their individual odds were -400, the parlay odds for all three would be -105. Therefore $200 on each team individually would win you $50, where $200 on the three-team parlay would win you $190.48.