I have log books going back years, probably 20+ books. I'm not a genetic freak and I couldn't have made the progress I've made in my physique without them. I actually looked back at a log book from a year ago last night - 1 year ago I was flat benching 405 for 10, now it's 430 for 10. 1 year ago I was rack deadlifting 460 for 10, now it's 500 for 10. 1 year ago I was military pressing 285 for 10, now it's 315 for 10. These aren't newbie gains and I'm not a young kid.
Consistently getting stronger is essential to consistently adding significant amounts of muscle. If you just want to look good to the general population then you probably don't need to log; if you want to be a freaky lean 250+lbs. then you better log.
There isn't one successful business - successful meaning revenue growth year over year - that doesn't track KPIs. Bodybuilding is no different. Barring the 0.001% genetic freaks, you're doing yourself a great disservice if you don't log and try to progress over the short, medium, and long-term. It's one of the main reasons people never reach their goals.