As Noy mentioned above, it all boils down to safety and I don't think I could have said it any better than he did.
Lets say you're flying a multi-engine airplane with someone in the right seat that is just as current and qualified as you are and have an engine failure right after takeoff. Knowing who does what is very essential. Are you going to fly the airplane while the other guy works the radios or are you both going to fight for control of the airplane as you Vmc roll it into the ground?
To expand on Rickair's comment, as far as future employers are concerned, it seems that the Part 1 definition of PIC is usually what they are looking for. For example, some don't consider logged PIC time as a safety pilot towards meeting the PIC qualifications they are looking for. I knew a guy that was sent home from an interview because 1.5 hrs of his 100.0 hrs of multi was done as a safety pilot. He came back and bought the time he needed to meet the mins and then later got the same job he was interviewing for.
Last edited by multipilot; 12-26-2008 at 07:50 AM.