The best reason is for health reasons. Rabbits can get reproductive cancers so spaying and neutering can give them a longer life span.
If they are not neutered the males will spray more.
Females usually get very aggressive and that is usually what makes people lose interest in the rabbit because it is harder to handle them.
I find that unaltered rabbits urine is stronger. Bunnies should be indoor bunnies because they make wonderful pets. They are pretty easy to litterbox train. We use a litter pan and untreated stove pellets. (never use clay based litter.) You can also use Feline pine, or horse bedding (the pellet type). We use ABM. Put it in the corner where they go the most.