In the early 1990s, a church music director sent me a video (commercially produced) of Nancy Allen and Kathleen Battle performing “Little David, Play on Your Harp” and wanted me to write out the harp part so it would sound just like their performance instead of the printed part he had rented or bought (which was arranged by an organist). It was listen, notate, rewind, listen, notate, check, change, etc., for hours. I boldly called Nancy Allen to ask about the part and she was surprised to learn about the published arrangement, so that was not good news to her. I finished my hand-written, pasted-together part with arcane markings only I could understand (this was also before I had music notation software) and did the performance. Weeks later the guy calls me and wants me to send him a copy of what I wrote. I really didn’t want to because I knew the arrangement was not authorized and, once he had it, he could hire someone else to play it instead of me. I never sent it and haven’t played it since. I still feel uneasy about the whole experience.
Nowadays, unless it’s something I really want to play or think I can use again, I don’t go to all that trouble, especially for an ensemble part. Do it sometimes for solo stuff.
Addendum: I did transcribe a harp solo from a Marx Bros. movie for a dear friend because she was performing onstage in the play, and the pages they gave her were from the rented full orchestral score from another part of the show and nothing like the original solo, which was never published. It was a fun exercise in dictation, done for love.