I just gave myself vertigo. A pleasant kind of vertigo, like the world has been lifted off my shoulders. I'll explain:
Yesterday I saw to my dismay, that I had made my entire map two - two - units too short on every level - that every set01 piece was sticking 2 units into the ceiling. That's basically 402 brushes that needs to be realigned (minus the ground floor brushes).
I knew enough about selections to do all of that in a very tense five minutes, and it compiled without leaks. (Thank you so much, Dark Radiant devs, for making an editor with such care for precision that you can align hundreds of brushes perfectly at once (which is not something I can say for Valve's Hammer editor, which has some serious issues on that front, which actually made me just quit it in disgust).) However, the result is that the entire level has now been stretched a barely noticable 2 units, and it will take some getting used to psychologically.
My workflow is basically running from a chain of disasters, eventually trying to seek shelter in former disasters. It's not ideal - it's just my life.
When I abandoned my first map, it was out of a typical mental breakdown, and so I returned to find a skybox void where the kitchen door should have been (due to a misplaced visportal) and two overlapping brushes Z-fighting on the kitchen floor.
I've now cleaned up the last bit of mess, by cleanly separating every floor into its own layer. Now I can finally work on each floor in peace.
...not that I really needed to. Once you get skilled enough, the orthographic messes, well, I'll let this video speak for itself:
Beams, beams, beams...
Support beams, and cross beams, and then beams to fixate the support beams to the cross beams. The more beams you have in a map, the better. There's walls, floors and ceilings, but the rest of the map is pretty much just beams. Beams makes a thief happy.