Not all of the window is usefull all of the time. Sometimes only the terminal half of the IDE is, sometimes just the editor half is. Same to the browser, sometimes you only need to look at the console and not the website (while testing something over the IDE). Resizing windows is actually way more annoying than just aranging them the right way so you can alway trigger the useful half.

I think most tilling WMs fails to realize how annoying windows that keep changing size are. If they do, the entire concept of automatic tiling seems way less useful.

You could fullscreen them, yeah. Just for gitui on my monitor, I find that 67% is both sufficient and enough, and keeping a little bit of the other window in sight helps maintain spatial context.

Besides, when it's something like runtime logs in a terminal, I sometimes keep the terminal maximized (to avoid line wrapping), but only leave it peeking out, so that I can switch to it if I notice something strange in the left side of the output.