I'm currently ironing out the kinks on a new system build, and trying to work out the best settings for various games I run. I'm running an Asus GTX 660, and it comes with a piece of software called GPU Tweak, which amongst other things, gives me a live, view of GPU usage, and a reading on what was the highest value reached in a session.

What is VID usage and FB usage? The values don't seem to go very high so, when would these be important?