You can feed it to them as a way to add more varieties to the diet in order to add more vitamins and minerals to it. You can feed fuzzies, which I think is better having solid bones. Quite frankly, I think they do benefit from eating the occasional mice because they are a good size lizard and probably needed a boost in vitamins and minerals every once in a while. I'm sure that's how their diet in the wild are like and that's why they are so big so they can pretty much eat any smaller animals (bugs, lizards and even rodents) and even plant life. It's easier to feed them something rich, like a small rodent, to nourish a huge body like that than eating hundred tiny bugs, which don't offer much in term of nutrition compared to vertebrate preys. A hole mouse is nutritionally complete and besides that, you don't want to limit you bearded's diet if you can help it. Their diet in captivity is already limited, so adding the occasional mice isn't bad at all. Just don't feed it too often and you'll be fine.