As far as I can remember, it was about keeping the tubs in good shape and clean, sorta like the canvas drop down on MGR's. Some others might have more information, we really didn't do on our show back then.
But I do remember another interesting thing, when they "parked" certain rides for overnight. Example would be the Roll O Plane parked at midpoint, or a Zipper. Saw Deggeller's Huss/Weber 1001 Nights parked/closed for the night all the way at the top, looked funny just sitting there in the air.