Shavings help control mud by soaking up moisture but wet material needs to be promptly picked up and replaced with fresh. Dry shavings are a fire hazard, and it's easy to lose grooming tools and other items in the loose surface. On windy days, shaving near doorways blow everywhere. It shifts underfoot and makes dust which can cover everything in the barn. Road base, a mixture of dirt and gravel, varies in composition depending on location.
Some types pack very hard while others remain loose and dusty.
It makes a good base for almost any kind of solid flooring. Gravel comes in various sizes. It drains extremely well and makes an good base for many types of solid flooring. Sharp gravel makes a more stable base than round gravel. Like sand, gravel is unstable and usually dusty, so is unsuitable as a finished floor.