I remember in Halo 3 when the heroic map pack went free, and suddenly, games were much faster to find and opponents of better quality. It's better for the community, as a whole. This is the altruistic side of the coin.

The business side of the coin (which is what you're looking for, I'm assuming) is that this is a great idea from a business stand point. Microsoft is no stranger to eating costs for a loss. The original xbox is a great example (sell the console for 299, it costs 400 some to produce) .

343 and MS have a PR problem.

MCC had a craptastic debut. Leaves a bad taste. This will encourage more people to play, to give them incentive to buy the game.

As for what you're not getting, we haven't seen any word on theater or forge. Also losing local co-op. Does that count?