I've used carve as a shortcut for making rooms.
Granted, they're always cramped, small rooms, but rooms nonetheless.
That is exactly the type of thing you should never use Carve for. The walls, floor, and ceiling will be made of weird wonky brushes that are far from optimal for the compiler and game engine.
There is nothing carve can do that clipping tool can't do better.
What if you have a ramp that is diagonal in two of the three viewscreens, and you want to make a railing out of brushes coming up from that ramp because no rail model will fit that ramp, and you don't want any of the brushes for the railing to be embedded in that ramp? The plane of the ramp is not orthogonal to any of the view screens, so the Clipping tool can't do the job, so using the ramp itself to carve the bottoms off of the rail support pole brushes is the only option. This exactly the situation in which I found myself years ago. Since the surface of the ramp is making a clean cut on the ends of the pole brushes, it shouldn't result in the usual problems associated with the Carve tool.
This does result in some off-grid vertices (but Clip can do this, too), so you don't dare move either ramp or rail after doing this, so if you must move them, you would need to re-do the carving.
The situation where carving has to be used because clipping is impossible is rare, but it can happen.