it will dramatically speed up map loading times *especially if you like to play on more than 1 planet.
PA do not save maps on HDD, they're generated on the fly in lobby and always stay in RAM. E.g when you save system PA only save it's generation settings and not actual geometry data so it's jue few kilobytes of data at most. Though when you press to "start" a game when map already generated there is some huge UI loading process going in background. All UI files are extremely small, but there is quite a lot of them so SSD speedup startup of 30 UI processes where each load quite a lot of JavaScript/CSS/images.
So where are these UI files located? I don't want other files in my SSD wasting space. (Using symlink/junction)
Mainly in "/media/ui/", but it's also read units blueprints and icons from "/media/pa/" which is largest directory in PA that is 1.4GB
By the way, does planetary annihilation work with symlinks/junction points? (Specifically with steam)
UI isn't part of Planetary Annihilation code and I pretty sure Google Chrome (Coherent UI is based on Chromium) should handle anything pretty well. Though it's always worked for me pretty well on Linux, but no idea about symlinks on Windows.