To my understanding the recover speed is how fast the machine will be ready to analyze the next target. I vaguely remember hearing that with the faster recovery speed is you sacrifice a little signal depth and ID accuracy but I might be wrong about that.
If you are hunting a open field with very few targets a slow recovery speed might be optimal. However, if you are in a trashy park or an spot loaded with iron where the signals on top of each other you might be better off with a faster recovery speed.
I have mine set at 4 or 5 usually but the best setting for you would depend on the places you hunt. Hope that helps (and is accurate).