I don't think its that big of an issue. Each dojo has their own etiquette regarding this. I have folded a visiting instructors hakama on several occasions. I have had it done for me, also.
When a student folds my hakama after class, it is usually so they know how to do it when they get theirs. Also, it frees me up to answer questions and get changed quickly so we can go have a "beer waza" after class.
In my dojos it is a utilitarian motive primarily and then out of respect.