I had a friend in high school who had amazing pitch recognition. I still remember being at band camp and watching him with a cassette player and a stack of manuscript paper transcribing the “Get Away” break from Chicago a measure or two at a time. He’d play a bar of music, then write down all the parts. It really ruined me because I assumed this was a binary thing, you either had it or you didn’t and didn’t realize it could be learned until I eventually learned it.

Perfect pitch is in no way necessary for this. Interval listening is sufficient. The additional benefit of perfect pitch would be, that your friend would know the basic key of the tune without first playing one note on the piano. For example, I don't have perfect pitch, but I can play along with any pop song immediately, without sheet music and without knowing the piece. I just have to press a few keys on the keyboard to find the root note.

Or both. You don't have to choose one or the other and I think the two skills could be very complementary.

With perfect pitch, you save yourself the five dollars for a tuning fork. In my forty years of experience as a musician, I have yet to encounter any other benefit.