The biggest thing would be that a game under playtest is likely to undergo drastic balance changes and potentially even changes to core gameplay, a review of a game in that early of a state would likely not reflect the finished product, and is unlikely to be updated or taken down when the game is released, this possibly poisoning public opinion with content that doesn’t reflect the actual game.
Gotta say though it’s kinda nice when you run an update to be able to tell ah yes KDE apps are being upgraded when you see the wall of Ks