Do you like data? Not everyone is obsessive…
After about 450 rounds, my Ruger Mark II slowly starts exhibiting reliability problems. Gunk around the bolt face/extractor and elsewhere. I now know when to expect to clean it, and can do it before any failure. Your personal experience on your own guns can tell you similar things if you keep records.
After 10k rounds, I should probably replace the recoil spring in most centre fire pistols. Or so the experts tell me. You want to follow a replacement schedule for springs and other wear parts, have to keep count.
Curiosity: how many thousands of rounds before this pistol breaks a vital part, wears the barrel smooth, otherwise gives up the ghost? It's a contest to see if you or the gun croaks first!
Do you use your guns in matches? The above considerations and more come into play, ensuring when you show up on the line that day, you can be fairly confident they will perform at peak. Because they're clean and functional and in-spec. and within the expected life cycle.
Are you training, whether for IPSC or ISSF and others, or just personally to improve your shooting in a regimented way? You can document your milestones: now after 7k rounds you're shooting 90% in the A zone. Or I doubled my practise to 1k rounds per week but not seeing improvements, might have to return to analyse fundamentals.
If you're serious, you should keep a shooter's diary (Google for some examples). Not only round count and score, but conditions, session goals and analysis, how you felt (energetic or coming down from a cold, confident, frustrated, gassy…); many factors affect how you shoot, and if you approach training like you're on the Olympic team, these should be recorded.
Will you be selling it later? Keep an accurate round count, then post it on the EE claiming only a tenth of what you've fired! Everybody does it.
