Vault horses intended for BDSM play typically have D-ring fixing points for ankle and wrist cuffs. They may also be adjustable, to cater to bound partners of different heights and may have removable legs for easy storage.
Some tops claim that a vault horse allows them to put their submissives in the best possible position for paddling. The bound person lays with their full weight against the comfortable padded top of the horse. This makes their buttocks relaxed and plump. As the furniture allows the submissive to relax into the sensations, it's a perfect piece of furniture for lengthy spanking sessions.