Like anything else with bearings, the good ones have less friction and are "stiffer" (i.e. little or no energy loss due to flexing)...the high-end recreational BBs are the best in my opinion, since they are fully sealed cartridge bearings that require zero maintenance and last for years. The top-shelf Campy and Dura Ace racing BBs pretty much assume you have a team mechanic repacking your ceramic bearings every time it rains.
I could see that too. Just curious - what's the advantage of a high end bottom bracket?
