It's not necessarily an excuse for failure.

If, on some level, you are looking to demonstrate fitness (perhaps as a signaling methods to potential mates), then if you visibly handicap yourself and STILL win, you have demonstrated MORE fitness then if you had won normally. If you expect to win even with the self-handicap, then it's not just a matter of making excuses.

I think this is similar to how very often a chess master when playing against a weaker player will "give them rook odds", start with only one rook instead of two. They still expect to win, but they know that if they can still win in that circumstance, then they have demonstrated what a strong player you are.