I usually replace at 5 years whether I need to or not. I’ve had a few catastrophic incidents (not in terms of data loss, but rather with just loss of computer) where I kept putting off the purchase, so I think it’s generally not a great idea to wait until it dies completely.
My quandary now is that my MBP (2014–I will hopefully skip the entire butterfly incident) is starting to show its age, especially with the Big Sur update. I’d rather wait for the M1 16" MBP, but I’m not sure I can…