IMO, it's partly good practice, partly placebo effect. And I "try" to excercise somethings during the offseason.
Namely fuel injected equipment, but only some. Boat is port injected. It goes away clean happy winterized and full maint in September and comes back out in my or June. 20 years of doing this. Can't run it without de winterizing.
EFI sleds, bikes, etc. Get maint and winter summer ization. Typically the do get started in the off season because it's easy and sometimes necessary to move them.
Small tools, generators, lawn equipment, saws etc get gas drained and run dry. Maint as needed and put up for the season. Or sometimes they get stabilized non eth or a dose of AV gas or race gas depending what's on hand when they are getting put to sleep for winter.
Vehicles, I have and have had vehicles that sit or get mothballed. Sometimes run, sometimes not.
Honestly the only real risk is carbs gumming up or varnishing. If a person has taken care of that and does good maint otherwise, there's no real "need" to excercise.
