Bedding is nice because it provides cushioning for the rabbits, but you don’t need bedding if the floor is solid and you have more comfy mats or blankets to put in the cage as well. Some people say bedding and litter are synonymous in some cases, so some people’s litter is actually labelled as bedding. If the floor of their cage is solid, even-grounded, and not wired/rough in any way, you don’t need the bedding. If it is or if you just want to provide comfort, you can sacrifice a shirt you don’t wear or buy a cheap fleece blanket or two to put on the cage floor for them to interact with and potentially snuggle with.

There is always the tendency for rabbits to pee on soft things, so the advantage to the latter option is you can easily wash those items, rather than throwing out bedding, which is wasteful.