It's one of those things that just sits there until something written to take advantage of it is used. I wonder if there is a list of floating point intensive 68k apps?

It wasn't until the first-person 3D games took off on the PC that FPU performance became important for the typical home user. 3D rendering, CAD, spreadsheets, and audio editing are all likely to make use of the FPU. I doubt you will run much on a Classic II that will get much use out of the FPU so it's probably not worth seeking one out, but if you have one kicking around, you may as well pop it in.