Let’s talk for a minute about being professional. I’m using the word “professional” as an adjective. If you are a professional, you have to act professional.
You want the gig to go smoothly, and you and everyone else want the group to sound good. If someone sounds not so great, and it’s obvious to everyone that’s true because that someone didn’t bother to look at the part, then we feel miffed. It doesn’t show respect for the music or for the rest of the group.
If we follow the Golden Rule—”Do unto others as you would have them do unto you”—you will show up prepared for the gig. It’s the essential professional quality, and it will get you more work in the future if you do show up prepared.
Being prepared is the greatest show of respect for your colleagues.
Period.