I've noticed that I tend to let my followers test out different equipment to see if they are more effective than other materials, or even just to see how different armor looks before I use it on my character. As Arch-Mage of the College, I've taken young J'Zargo under my wing to do a few quests. My Battlemage is lvl 49, so some of the enemies we face are pretty tough for him. We pieced together a full set of glass armor, which I improved to Legendary, and gave it to him. Also gave him the old Arch-Mage's amulet and a ring of Eminent Health. Even with his novice spells, he's faring much better now that he has some protection. That glass armor is also quite eye-pleasing and I'm thinking about taking it from him when I finally dismiss him. Anyone else use their "mules" to try out new weapons or armor before using it themselves?

On a somewhat related note, if I buy higher level spellbooks that I don't need and give them to J'Zargo (or another mage follower), will they read them to improve themselves or would it be a waste of septims?