Originally posted by Dimyell:

Just curious, what does the rested bufff do? Increase HP regen? Because from what i've seen the bonus HP from food can be insane.

Rested: +50% health regen, +100% stamina regen, +100% Eitr regen (you'll discover this much later)

You can see the effects of any buffs/debuffs on you by opening your inventory and clicking the raven icon near the top-right window.