The Kodak lab in Vancouver BC used to have a large booth at our annual fair - the Pacific National Exhibition.
They used to have 8 slide projectors, 4 dissolve units (I think) and 4 big screens, and the staff at the lab contributed slides for projection at the fair.
Two weeks long, for 12 hours each day, those projectors would show each of (120?) slides over and over for about 10 seconds each time.
Most were Kodachrome, but some were Ektachrome.
At the end of the fair, the slides would go back to the staff member who supplied them, essentially none the worse for wear.
My Dad used to man the booth each year. On more then one occasion, I saw my (then cute) face up on one or more of those screens.