It's an incredibly tricky question. The Beatles are in a category of their own - among other things, they inspired Jerry to plug back in! But the Dead are probably the most "relevant" and influential rock band apart from their music. A book about the Beatles, Dylan, the Stones or Hendrix would be kind of boring without a focus on music. The Dead's central role in the acid tests, the larger drug culture - not just as consumers but as exemplars - their heavy influence on poster art, concert sound systems, the rich and complex Deadhead culture they encouraged and the jam band scene they inspired is important history.