With my very limited experience so far my first choice for QT/hospital tanks would multiple smaller tanks rather than 1 large tank. I have 2 - 20 longs and a 50. I've yet to use the 50 gal. If something went south and you had to move and house fish somewhere, it would seem better (again in my limited experience) to put aggressive-ish that don't do well with others in a smaller but longish tank (e.g.. tangs) by themselves and happy schooling, peaceful fish, in another tank or 2. Smaller tanks are easier to perform water changes in, so if the tank transfer method is for you, then that's a bonus. Smaller water volume makes it easier to treat with meds, you don't need as much. If 1 fish needs a rest/hospitalization, you're not running a 70 gal when a 20 would do.
Downside is, it's a smaller tank. Ammonia needs to be watched closer than in a big tank. And it would be hard to house fish that get a bit stressed with other fish in a confined space, therefore I'd opt to put them by themselves. Now if you had 30 Tangs in your main display, that could be a problem
Anyway, that's my $0.02
Hadn't seen it expressed yet, maybe there's a reason....