Lolwut? I can't hit a shit with xbow if I have 1wpf (and I had 1wpf yesterday after I retired from shielder).
And I am not talking about using crossbow as a shotgun, because it isn't meant to be used that way - I am talking about shoting to targets 10+ meters far from me.
For me, it seems to increase dmg a bit, but maybe it is "only" a feeling. Well, afaik, all weapons' wpf are increasing their dmg...