Play the Ink!
Studio musicians are an interesting bunch. Highly trained, incredibly talented, able to play almost anything, funny, disciplined, and amazingly dependable. They show up on time, ready to go, and usually the first take is perfect. Then it just gest better.
They also like to make suggestions about things might be improved. So we have an expression in our studio: "Play the ink." It means read exactly the notes the composer put on the page before you start making suggestions as to how it might be improved.
The exception is jazz. Most of our jazz tracks are pretty much planned out in advance - 4 bar intro of some sort, then "play the head" (play the main theme as written), then "blow two choruses" (play an improvised solo over the chord pattern twice) and play the ending. Everybody has a written part for the head, the theme and the ending, we decide in advance who will solo in each of the two choruses, and we're ready to record.
Dixieland is different. The intro and ending may (or may not) be written out, but otherwise everybody is on their own, improvising their own parts over the written chord progression. It's never the same tune twice, and you can tell the musicians love it. Just listen to the enthusiasm in this track, especially the trombone slide about seven seconds in. Pure genius. I could never write a part like that!