Originally Posted by Thaurin
There is a reason, which is backup. If you delete an app, your saved games will also be gone. With iCloud support, they'll still be there. But I agree, across device save games is the most important use of iCloud saving.

That may be true of iOS devices, but deleting a game from a Mac does not take the saves with it. If they're going to the trouble of adding cloud support to the Mac version, I have to believe that cross-platform saving is the reason.