Experienced well-rounded employees can mostly take care of themselves (and know when to say "no"). It's the new-hires and rough-around-the-edges people that require more hand holding and can benefit more greatly from a manager.
Yes, they can. But that distracts us from our core job: writing code.
A good manager can get others off your back much quicker and shield you from the political fallout that can occur - essentially being the bad guy for you.
