I've not been asked by any of my T's. I have been asked by my family doc and GYN/OB and have been willing, usually, to allow them to observe or do, depending on what needed to be done. One medical student followed me for my entire pregnancy for reasons I'm not real clear about, probably a class assignment.

Going from a dyad to a three persons in the room is a big difference. If the student could sit behind me or way off to the side, I might be willing. It's possible something about the situation might be useful to me, such as perhaps I'd be a little more focused/observational of myself given the observer in the room. I also believe in the educational part of it for the student and think a student could learn something from live observing a real therapy session.