An ARS has a faster knowledge gain rate and some other desirable characteristics (immune to insta-kills, etc) so it's not a bad thing to have just for your regular knowledge gathering. They're wretchedly slow, though, and you don't lose anything (except pride) if it gets scragged, so you can just capture it to get the ship tech and then forget about it.
I always make sure to bring them back to my homeworld intact, though. In your face, malignant AI.