The age old question
"In a crash, do you want to stay on the bike or get tossed clear?"
In my 3 crashes between 2009 and 2015, I think I'd been better if I was seatbelted down. The second and third impacts are what caused the major damages.
The Goldwing crash I went thru the windshield and hit the ground hard, the bike just laid over.
The 2010 Burgman crash when I low sided and then the tires caught and flipped me up and slammed me into the fender followed by the Burgman slamming into me it may have gone a bit different.
The 2015 Burgman crash after the first impact of the concrete barrier I hit the ground hard and slid over 450 feet on the rummble strips. A seatbelt may have changed things, may have been worse.