I obviously know what the infield fly rule prevents.
I'm just asking why we need to prevent fly ball double plays. If it's an aesthetics thing, what makes the aesthetics bad? Everyone's fine with the other double play forms.
Edit -
Also, there's another situation in which the defense benefits from not making a play:
Runner on third, less than two outs, deep fly ball into playable foul territory. If the game situation is such that getting an out is not worth sacrificing a run (i.e., the defense is leading by one run late), the defense should let the ball drop.