Honestly? There are none for the consumer. Sure you might get some minor things like other players in your "single player" experience, but that is vastly outweighed by the benefits developers and publishers enjoy from this model.
They're essentially selling you a ticking time bomb, one that requires you to get permission from them to even play your game. This means that, in the not too distant future, when the servers for the game go down (or the company goes bankrupt/lose the IP/whatever) you will not be able to enjoy that game.
Developers and publishers want to turn gaming into a service, rather than the traditional setup where beyond the point of sale they're not getting any more money from you. Meanwhile with this new setup becoming standard, people are forced to view your ads, view your online marketplace (with tiered pricing!), and buy new copies as early as possible to enjoy the game for as long as possible.
Pay attention to the next few months as nearly industry figure and company will spin this as an evolution in gaming, the next step in advancing the medium.