I have a fancy tent that's really nice and very fast to pack in. I realized for the average summer vacation, a total of 2,208 hours, if I'm doing the most camping I've ever actually done in the USA, then I'm going to have that tent in use for ~252h (11%). The rest of the year, it's probably going to be in storage (3%). I wouldn't go camping MORE if I had a RTT. So that means 97% of the time, it's going to sit there unused, which is my argument against them, and that's the best case scenario. The closer scenario is 1% usage, 99% storage. I'd rent camping gear if it wasn't such a pain in the ass to do it.
RTT's where I am don't make sense because a good chunk of parking garages are somewhere between 6'8" and 6'11" in height. So it's somewhat rare to see them, and if you do, they're generally not allowed in parking garages. But it's really weird seeing something like that strapped to a Prius.
I like the convenience of having it mounted on a solid base already. In the PNW, it's wet here, so having a RTT would allow you to easily pitch it on a surface guaranteed not to flood. Additionally, if you were parked on the street near where I work and it had rained while camping, you could zip out, pop the tent up so it can dry out while having lunch, and then pack it in really fast. I haven't taken a good look, but one of the problems I had with a camping cot is airflow underneath, and the PNW is also a COLD place, so I think that's a vote against RTT's. However there are some people who use something similar when it's snow season, so I guess it's not that bad?
I'm also a fan of ground side camping, but I previously used a tarp for the longest time. For the same reason as I don't use a cot anymore, I don't like hammocks. Yes I know you can get quilts, it only solves half the problem of hammocks for me. I sleep better on a flat surface.