i.e. are there new experiences that you can have with this temporary tag-along player that will mix up your existing gameplay and add flavor?
well, its another spear at your back. if they have special skills (warrior, trader etc), you can learn from them. and of course its a "mule" to carry treasure back from the dungeon. IE the usual advantages you get from an additional party member. being able to learn skills is about the only special thing. but in skyrim you can get members of the companions as followers, and thus have a follower who can train you.
as i said, the reward is the prime motivator. a temporary follower is nice, but the reward is the real benefit to the player. and the quest rewards are quite generous. i seem to have found that happy spot where the treasure is quite big, but not monty haul. makes quest treasures in skyrim and fallout look like a joke. i save whiterun from a dragon and you give me an axe not even worth 1000 gold?