I laid out a couple of Trang chapters today using skinnier margins. Wow. It is like a thousand times easier to lay out a book this way. You have far fewer problems with loose lines, and you don't have to break nearly as many words. Seriously, it may be even easier than laying out a large-print book. So, it's easier, it costs less--I'm definitely going to be using minimal margins from now on.

So far I haven't had to push a line down (!), but if I do, I can in fact use invisible text--the test text did not show up in the proof.

ETA: I'm really pleased with how much faster this is going. I think it's because there are more letters per line, so if you're a few letters short, it doesn't look as dramatic. Like, if you have 20-character lines, but you only have 15 characters on a particular line because a word was too long and moved down to the next line, it looks really bad. But if you only have 35 characters on a 40-character line, it's just not as noticeable, and you don't need to move Heaven and Earth to fix it.

Obviously, the new layout is going to be much shorter, and fewer pages mean fewer places where the bottom lines don't line up. So that's also going a lot faster.