Long stem fiber wears down the molars properly. A lot of rabbits on pellet only diets have overgrown molars if you really looked at them. This can become a health issue but it usually goes unnoticed because the rabbits adapt and I can't say a slight risk of overgrown molars from hay cubes instead is worth taking a rabbit out of a good home. While I do not prefer it 1000s are living symptom free on pellets only.