When I first started modelling in Blender I didn’t like the thought of subsurfing when I could make all the faces myself and know that they were made to my exact specs, but the little Mars colony I was building quickly got out of hand, and even in wireframe mode I was getting about 12 FPS when spinning the camera around.
Then I got onto some tutorials that recommend subsurfing and I started modelling with the simplest geometries I could get away with, and it certainly makes on-screen objects a lot easier to pick through.
Is it just down to what your computer can handle or does subsurfing reduce render quality in some way?
Subsurf is not for game modeling (you mentioned fps). Unless you are going high poly and plan on baking a normal map. I use subsurf on almost every model I do, it doesn’t affect render quality at all, it is just a technque that allows you to have a simple model appear more complex. Less verts = less work.
As far as I can tell subsurfing gives the same render quality as if you were to create everything yourself. After modeling for a while switching between subsurf on/off you will learn how to compensate and accurately model with it. It just becomes second nature.