I always point to Mississippi Half Step to show what Bobby is about. His parts often aren't necessary but what he adds is great. In a band with a bass player like Phil (what's the old joke? Phil Lesh is playing? Cool, who's playing bass?), a keyboard player, two guitars, and two drummers, it's hard to find space to add meaningful parts without completely mucking it up. There's some recording of Half Step from Englishtown '77 (not sure if it's the Dick's Picck) that you can put the balance to one side and clearly hear what Bobby is doing. It's fantastic.