I don't know whether it uses data compression and whether that has to do with it, but when downloading the game fresh, it seems to only download the size of the data file, so I would assume not. I monitor my SSD writes, and I just started the PTU-patching from 3.1.4 to 3.2 which was shown as ~8 GB, but the amount of SSD writes registered is roughly four times as much! I'm wondering why that is. I hope it's not some unnecessarily complicated writing algorithm.