Depends what you shoot.
Lightroom is the bread-and-butter of the event, wedding and sports photographer, and other high-volume work. PS is the tool of the landscape photographer, the studio/fashion/advertising photographer and the fine art photographer.
Definitely depends on what you shoot. My style of photography isn't all that refined, so I can get away with just the tools available in LR. Doesn't have all that much to do with high volume and it's cataloging features, but I'm very comfortable with the raw development options and localized adjustment options it offers. In 95% of the cases for me that's enough.