[feoren]

You're right that it's not at all necessary for being a professional musician, but it doesn't hurt either. It's particularly helpful if you want to be able to sit down and play a song you know from memory in its original key. More of party trick than anything else. It seems to me that having perfect pitch is more of an indicator that your brain is highly tuned to remembering pitches accurately -- it's not that perfect pitch itself helps, but that people with perfect pitch just also have very good ears in general.