Golf Ball Research. Check out the findings of a Golf Digest study from a few years back:
"Golf Balls are likely to be lost or damaged before they wear out. According to Golf Digest, unless there is visible damage to the cover, the average golf ball should last at least seven full 18-hole rounds without any degradation in performance. A little lost paint or other marks that leave the contours of the cover intact are acceptable, but once there is a scuff on the cover that feels rough to the touch it is time to take the ball out of play."
Which golf ball I use (brand, new or used, etc) is a last second decision just before I tee off. Many times it depends on where I'm playing (nice courses tend to get tour performance balls) or how early in the season it is. If it's early and the greens are dormant, I play a cheaper distance ball.
But I realized tonight that I've used the same golf ball for 3 rounds of golf. Yeah to me for not losing it! But it's starting to look a little dingy and has a couple nicks on it. According to Golf Digest's research, I should pull that ball in favor of a new one. So I guess I will.
But when do you replace a golf ball you have in place? Do you use a new one each round?