Specifics on surfaces?

After doing a bit of studying, and using the mighty search function as best I could, I've managed to get a decent grip of the concept of surfaces, but there's something I still don't quite understand.

I understand that overuse of -anything- would mean significant slowdown, but from the way people talk about it, surfaces bog things down more than anything else. This is what confuses me.

I suppose my question is.. I know that surfaces slow things down.. but what -specifically- does it slow down? Does it eat up Memory? Vram? Processing power? Does it slow down programs as a whole, or does it just harm the speed of certain functions?

If I'm being vague, I'll refine my questions a little. For now, I go to try and test some things myself. Any assistance is appreciated.

Thank you.

Each time the gfx card hits a new surface, there is some additional 'housekeeping' to do. So, each surface will lower your FPS a little whislt the gfx card sorts itself out. However, although you should minimise surfaces, dont go overboard about it - that would be like saying I won't use any polygons because each one lowers my FPS!!

Rhy :)