The greatest benefit of sharing an IP address with a large number of other people all browsing the same hundred or so websites at the same time is ad saturation. Adsearch auctions still have no idea how to account for a large number of hits that are clearly human, but also trigger frequency protections — so you just see no ads after a while. Nice. (Incidentally, nobody in the world has any clear idea how to distinguish robots from humans, so… have fun with that if your business model depends on any aspect of this.)
A second benefit is a super fast, constantly refreshed, broadly populated DNS cache on the local network.