The fact is, parlaying your bets in a correct manner can help you to dramatically reduce the downside risk to your bankroll. Say two bettors have the same 15 bets at the same time. Now, say they have one of those hellish days that make a sports bettor feel like King Midas in reverse. You know those days. We all have them.
Nothing goes right.
The parlay bettor has limited his risk to five units, no matter how bad things get. The 'standard' bettor has risked fifteen units, - three times as many as the parlay bettor. The parlay bettor stands to win much more, depending, of course, on how he grouped his bets. Sometimes a parlay bettor will get lucky and happen to group all his winners into the same parlay and all his losers into another parlay, other times he'll get unlucky and manage to group his winners with losers and lose all his parlays. The luck of how the bets are grouped will even out over the long haul.