Our horses have several “rolling” spots in their pasture. Generally they eschew the clean, dry grass for a mud pit or at least a lot of dirt.
Freedom rolls several times a day, as far as I can tell — immediately before I want to ride (that’s in the muddy spot), immediately after I’ve hosed him down (that’s in the dry spot) and any other time he thinks that it would be better to be dirty!
Depends on the weather. If it’s windy, he rolls in mud, to plaster his coat down – I think it’s windproofing. If it’s dry, he has a dust bath. If it’s hot, he rolls first thing in the morning in wet grass to wet his coat. He usually flips over a few times, even if he has to roll uphill to do it 🙂
My horse does not roll at all, ever. He’s a weirdo.