Never, but one employer tried.
When I worked at KPMG, they tried to get me to share a hotel with an other person for the off-site orientation. I deliberately cancelled my stay with that hotel, and booked one with another hotel across the street. Pretty nervey for someone just starting, but I had actually been with the firm for two years. Yes, they insisted that I MUST attend orientation, even though I had dodged it for two years. HR tried to complain, saying that having a room mate is an essential part of making a connection with fellow workers at the firm. To wit, I mentioned that I have been with the company for two years, so if I have not done it by now...it ain't happening.
I worked in Korea with natives working for KPMG, and they were all forced to share rooms when travelling. The partner would get everyone to double up, then bill double for the rooms. Unethical of course, but not too surprising, considering how he treated his employees.
I have travelled a lot, and if my employer cannot afford to pay for my own room, they cannot afford me.