It has been said that a shooter should hold the gun so that it rests on the skeletal structure. Bones will not fatigue like muscles. The fist and the palm, and variations on these, allow the gun to rest directly on the bone structure and you have less of a problem with muscle fatigue.
I personally started out using my fingertips, due to the fact that it raised the rifle inline with my head. However, after moving to the palm I have found that my scores have definitely increased, and I can shoot more standardized scores throughout a day long competition.
In the end, it really is what is comfortable to you. However, you do see many top shooters using the skeletal structure technique and many of will keep to the same stance the whole way through a match.