Hand position variation is what I like them for. Although, I am swapping them out for some risers and reserving the bullhorns for track use (I don't like track drops).
My justification to swapping for some big, wide risers is that I plan on racing the Sea Otter Clasic (XC MTB) next year, and I want a more "MTB" position. I doubt it'll make a difference... secretly I want to tarck out my bike since it is one of the more jonzin' bikes I own.