From another thread:


Quote Originally Posted by FourLengthsClear View Post

Parlays at true odds where the individual legs have +EV compound the +EV. Consider two bets at 2.00 (+100) where the fair line should be 1.909 (-110), these would offer an edge of 4.77% as straight bets or 9.76% (1.0477^2) as a two-teamer.

That increased +EV comes at the cost however of a lower winning percentage and, by extension, increased variance. Maximising growth/ROI would actually be achieved by two combining straight bets with a two-teamer.

The main reasons for parlays being considered sucker bets are that they often pay less than true odds and far more importantly most bets made in reality have -EV and in these cases the bettor is a victim of both the compound effect and increased variance.