I don't really care about space all that much, but packages I build tend to get uploaded and the people downloading them may not have fast internet. Meanwhile, packages built by my AUR helper I care about speed (seriously, it takes ages to compress then immediately decompress firefox). The problem isn't that I want to optimize for one or the other, it's that AUR helpers generally have a different need than I do when building my packages myself, but for some reason AUR helpers don't override the compression setting for just their install. Probably due to caching like I said which means they can't assume everyone will want compression off all the time, but I'm not sure, that's just a guess.