Who changes sparkplugs at 8K miles? Or air filters at 12K? Or even valve inspections every 16K miles?
That'd be me.
I keep a log (on Access) and record everything I've done. It lets me know when things are due to be serviced - by date and by mileage. I'm not one to play Russian Roulette with our safety. I'll inspect and if anything needs doing according to date or mileage, I do it.
Except - spark plugs have a tried and tested lifetime beyond which they could fail - eg crack, burn out, fail electrically. My superior knowledge of such things is non-existent. So they get changed on time. But 16k is the interval, not 8k.
And Oil / Filters. These tend to get changed before 8K. I can usually feel a difference before then.
And Air Filters. Always get inspected. Happy to clean them and use them a bit longer if the dust is dry and it will blow out with compressed air without doing any damage. But I note from my logs that I have only ever gone over 16K once - and changed it out at 21K with a clean up in between.
Valve Clearances. Engine noises niggle, so I tend to check them on or before time - but I usually wait until winter when I can take my time without it getting in the way of riding.
Tyres - 5000 miles. I
never ride if they have reached the wear bars. I once mis-judged how much life was left before a 2000 mile tour. I monitored them when they were getting close to the limit, and thought that I would still make it home. In theory, the last half mm should have done 500 miles. After 50 it had gone. I left the bike in Scotland, caught the train and went back with the trailer. It cost more than the price of two sets of tyres to do that. I only get 5000 miles from a set on the 1300. So now if I have already done 3000 miles, I'll be thinking very hard before using them on a 1600 mile tour. It's cheaper and safer to switch them out.