This is a complicated question and admittedly I know just enough about it to be dangerous...but here's my take...volume up front prevents pitch polling and helps keeps the bow up increasing the speed potential and decreasing the sensitivity to wave height. Volume in the center will help with tacking ease allowing the boat a fat middle point to pivot on. Volume in the rear helps the boat plane downwind. Rocker and daggerboard position affect tacking and upwind efficiency. More volume / flatter sections affect drag. Hull shape is a balance of all of these variables.
On a displacement hull, the speed potential is linked to the fineness ratio. For a given length the narrower the hull the faster it can go. Cat hulls are not fully dispacement though so this is only partialy true. Increased volume in general allows the boat handle larger crew weights, which in turn can ballance the horse power from the sail plan and provide better performance. This only works up to a certain point and too much volume will begin to slow you down eventually.
Jake pointed out the advantages of volume. Contra to that: too much volume up front provides bad pressure distribution along the hull and is slow. Too much in the middle and the boat wants to teeter fore and aft and is very difficult to keep in trim fore and aft. Too much volume in the rear and the transom sticks in waves and wants to trip forward.
Good luck in inerpreting any of these in a real world situation.
