What aside from butts being very painful and carving your eyes and face up machete style and making you very groggy you mean? Well if you have to constantly be on the look out for three weapons instead of two, one of which hurts like hell when it crashes into your face as you're being hit by one of the hardest parts of the human body (I've been butted hard before and I can assure you it was no laughing matter), obviously that is going to make you very wary of being caught by it and therefore affect your concentration and prevent you from implementing your game plan sometimes. It'll also demoralize you too if your opponent is allowed to keep doing it by a conveniently blind referee. I saw that Evander Holyfield video in the Classic the other day. Great fighter but what a cheating POS. Another ''devout Christian'' billy goat. I'm glad Tyson bit part of his ear off. Granted Tyson was a dirty SOB too though.
Psychological advantage, your'e cheating, getting away with it and it thrown them totally off their game. And inflicting pain.
The advantage of putting Butter on your head is there gloves slide of your head on impact. Olive oil is healthier and better for the skin though.