It adds a TON of new features, from optionally making Tolfdir arch-mage to experiments and actual lessons around the college that give you experience.
Honestly, I wouldn’t even consider doing the college quests without this mod. I highly recommend reading through this whole post even though it’s long. Here are some of my favourites (all of these may be used together).
I just started a mage playthrough, which is very different than my standard sneak-thief, so I downloaded a ton of mods to make the experience more interesting (since vanilla magic is so lackluster).