Generators need exercised regularly to stay ready for when you need them; particularly diesels. I have a couple of them. The main one is an air-cooled diesel, military MEP-002A that does an excellent job of tuning diesel into decibels as the saying goes, but it will run 24-7 with minimal issues. I do load-bank it for about 4 hours every 5 months or so. Runs the whole place, 220v well pump, air-conditioning and the whole deal. It is very important to let those warm up to prevent the engine from wet-stacking from running too cool under no load conditions. Also have a couple of parts units in case anything does wear out, but it's very dependable. I backfeed that one from the subpanel in the machine shed so I don't even hear it from the house. After a derecho a couple of years ago and 5 days without power, it was nice to have.
The other generator is a small, Honda eu2000i, suitcase type generator. It comes in really handy for powering up anything 120v and is almost easier using that than dragging an extension cord for remote work; battery chargers and the like. And it's a fuel sipper and super quiet. During the derecho I ran that one through the night just to keep some fans and the fridge running. Saved a lot of fuel that way. The problem with the Honda is that it is so fuel efficient that it doesn't prime well, and is a bitch to start after sitting for more than a month or two. It really should have been designed with a fuel primer bulb. But after it has been primed and started once, it always starts on the first pull.