Advantage for a single bet is that you are only faced with one side risk based on your single pick of team if It is sport bet. Your bet outcome also displaces immediately the single game is over so you don't have to hold back until other teams have to finish while disadvantage is that you will have to chase high odds to make good profits while risk to loose is a bit minimal

In parlay bet strategy your maximizes your risks dependently on every single teams outcome but the advantage is that you can pick lower odds and in sum is a high odd which can also give you good profits if you wins.