The barrel stands in for the horse.
If I was smart, I would “winter” in Florida like many performers. But home is here in the sometimes-snowy-NorthEast—so I’m grateful for the barrel for times I don’t want to practice with my horse.
Though stationary, the barrel isn’t as accomodating as a horse. Your head fits into the curve of a horse’s neck, whereas, on the barrel, you must resign your head to jutting at an odd angle to your spine.