A few months ago I was hanging out at a local studio, just checking out a friend's recording session .. there were live musicians performing most of the tracks in the studio that day.
One song was kind of a slow LA shuffle thing, and the drummer was fine, but on this particlar tune his playing sounded just a hair less confident than his performance on the other tunes. This was not very obvious, in fact it wasn't mentioned in the recording room at all - no exchanging of looks between people or anything like that. Everybody seemed pretty comfortable with it anyway. Of course, not everybody in the room might have picked it up from the same angle that I did, or maybe not all all - who knows.
But the drummer came in to the recording room and said that "hey guys, I can't do this kinda of tune, or at least do this groove any justice. I'd like to call in John to do it for me. Are you ok with that?" And everybody was, and this other drummer John showed up to do one tune and he did that groove a bit better.
Now, seen from the "employer's" point of view, how do you guys look upon such a thing? Sure enough it was humble and a rather cool thing to do. This other drummer John, was nobody that was a friend of anybody in the studio that day and of course the first drummer got to pay him a bit of the money he was getting for playing. Bringing John in caused a delay of about 1 hour but getting a better track down on tape and the first drummer also made the producer shine more.
Would we, as composers or arrangers do the same thing? bringing another guy in if we thought he might do just this one thing better then ourselves, to hopefully make the producer shine more? or would we be cautious to not introduce another talent to our employer, a talent that possibly could take our place if the producer wanted some work done while we're on Hawaii for a week? I've never done it myself, and I'm not sure I would.
This kind of scenario should also be happening in similar ways in other situationes .. so feel free to speculate ..