Go look at the size of your MLB 16 install on your HDD and then go see what the download will be for MLB 17....They are in same ballpark (no pun intended).
Also quick Google search confirms what I said.
The point of "needing" the disc after you install it is obvious. You bought the game and they do not want you sharing the game with anyone else. It is a restriction, put there on purpose....not an oversight.

we get it on the 27th
Comment