because the PFS is never constant, and having it at 60 means it will dip to 40, or 30, or less. if you have it at 36, it will start at 36, but will dip when things start to happen. so best to have your max fps set to really high, so if it drops, it has a lot of room to fall.

you can totally tell the difference if you have the two settings on, one after the other. first play at 36fps for a while. then switch to 60fps. you will see crisper movement for your char, other chars, mobs and even the environment around you.