Well if I keep the ball in play.. I will play the same ball until it has damages on it.
With my previous driver, (which I babied given the price), I noticed some scuffs on the face like I had hit it through the dirt or something. It was then that it occurred to me that a scuffed ball will ding the face of your driver/woods. So as long as the ball has no defects I'll keep driving it. After that I'll swap it for a new one.
However it doesn't mean I toss the ball completely. A small ding in the ball or piece of the cover the size of a head of a tack sticking up I will just peel off and play on holes were I'd T up with an iron. But say it lands out of bounds, or hits a tree, it will usually be damaged to the point I wouldn't play it any more. Thats how I determine when a ball is ready for the bin, or a very intimidating water hazard hole