I know for fiberglass "cruiser" boats that are on the water full time (in a slip), bottom paint is a must for several reasons, one very important one being to prohibit the growth of mussels on the hull.
I looked at my hull in early October - I have zero mussels anywhere on the hull where it is painted. I have mussels everywhere else where metal fittings are not painted - thru hulls, trim tabs, shafts/rudders/prop nuts. -Doug
I'm painting my hull this spring with Pettit Hydrocoat, ablative type of paint. Boat sits on trailer in winter and at the marina for summer, so this paint is the best of both worlds. I will use another paint type for the underwater metal work. I'm just wondering what others are doing.
FYI former saltwater sailor here, so its nothing new to me, but I haven't seen any threads about using bottom paints.