It's certainly not VITAL to your physique. I can't imagine a scenario in which a multivitamin enhances the physique much, unless there are deficiencies. It would be more accurate to say vital to your overall health. Even then, a balanced and varied diet can do the same thing as a multivitamin, and probably better.
That said, we're not all eating a perfect diet, and a multi can fill in the gaps. I personally have been sitting on a pile of G N C vitamins that I stocked up on when I worked there (couldn't you tell from the vitamin shtick?), but there are lots of better options out there.