In my case the arranger allows me to play my jobs and not have to worry about the mood of another band member or singer that wants to change the key to an impossable key for the horn man,
or 1000 other reasons I am a pro,and have made my living playing
for many years and after playing with every body and nobody, I
choose nobody. I always show up on time, wear the right clothes,
can play in any key and never get an argument about it. That is nice after all the decades I have done it the other way

MEL