Father: Merry Christmas son!
Son: Where's my present I dont see it anywhere?
Father: Ill download you whatever game onto your PS3 or 360!
Son: Ok, the game i want is 30gb big and i dont have enough space so we'll have to buy a new HDD and stores are closed today so we'll have to wait and buy it tomorrow.
(The next day....)
Father: Ok i just bought you a new HDD now lets download your new game!
Son: Yea thanks dad! We only have a 2 GB bandwidth and its an extra $2 per GB that exceeds it.
Father: um...no problem son its still your Christmas present!
Son: Since we cant afford the fastest internet its going to take 5 days to finish downloading it.
Father: um.....Happy New Years!!!
A situation that can easily happen, and could've been easier just by having the game on disc.
Again I refer you to the "kiosk" option.
But as others have already said as well, if MS could just release the install to harddrive option that would allow only the first disc to be needed to play, that'd be another great alternative.