Lots of Commander brews use their graveyard as a second hand, so you don't want normal milling filling it
And cards like Broodrage Mycoid only care if its controller Descended that turn at all
Noctis, Prince of Lucis' graveyard interaction is particularly powerful because you can use it any number of times on your turn, and life is a bountiful resource in Commander
We have Blazemire Verge, Hushwood Verge, Thornspire Verge, Floodfarm Verge, and Gloomlake Verge which all tap for one color of mana, but tap for a second if you have a land of a certain type
Wizards is releasing a special North America-exclusive version of the Limit Break Commander Deck
Magecraft even gives you a pest for the copy itself, so you end up making a profit of one token