I have a center cockpit on my Searunner 25 trimaran, and love it. Here's a short list of advantages:
1.) With the mast (almost) in the cockpit, singlehanded reefing is easier because I don't have to leave the cockpit to secure the main.
2.) A trimaran's center hull is narrow, so having 2 shorter cabin trunks and the center cockpit I don't have to shuffle sideways or stoop and scramble down a long narrow salon.
3.) Again, trimaran-specific, but keeping the heavy stuff in the middle makes the boat move easier over waves.
4.) A high center cockpit on a small boat leaves lots of room below the sole for tankage, motor, and other heavy or smelly stuff you don't really want under your bunk or settee.
5.) Centerboard is out of the way under the cockpit, not in the middle of the salon.
6.) The head can be a long way from the galley
a.) higher freeboard & more windage
b.) more complex steering (tiller is not really an option, outboard placement is a problem)