I've noticed recently that repeatedly, the install dialog shows wrong info on how big the game will be wnen installed.
At first, I thought it was a problem with the game itself (in this case, Judgment: Apocalypse Survival, reported 5GB, actually 3GB) but then I noticed it with more and more games, like Pillars of Eternity (reported 41GB, actually 25GB) or Obduction (reported 14GB, actually 6GB).
Those are substantial differences! And it wouldn't be so bad, except if reported size is bigger than total free space on the disk, it refuses to install.