Haha I’ve seen some pretty shot systems! Exchange was the stuff of nightmares, back in the day.
Desktop is not designed to be a portable installation, right now. It will install to the locations I mentioned before, and consume some system/default drive space. The goal is to provide a system that supports everyone - if there is an issue with the amount being used on the system drive in recent versions (>= 0.4.0), please speak up!