There are three benefits I see to getting MCC on disc.
1) Pure collectibility and having the case on the shelf
2) Selling the retailer exclusive DLC to bring down the cost of the game or just to have the DLC (but that's not very cheap-ass like)
3) Getting it at Best Buy for 20% off + $10 in reward cash for use later
Guess I'll go the physical route, once I get my $10 from Sunset Overdrive and save the MS $ for the season pass/DLC, if any.