This is a plethora of styles and situations. Grapevine is what we called in South Carolina a "beach band" - there are few charts, and everything is done by ear. I was sitting in for their regular keyboard guy - who had moved to guitar because their regular guitarist couldn't make it.
I'll be with the Joey Stuckey band in Cordele playing jazz in a trio setting Friday - with some homemade charts that serve as reminders. They are definitely NOT note-for-note (in some cases, not even chord-for-chord!).
Earle Barnette's group plays a more traditional form of jazz - it's a small ensemble, with charts that look pretty good. Lot's of chance for improv, but not as many as in a trio setting.
................and then there's tom&co, which will have the usual personnel changes that happen week to week, and will have some new praise and worship stuff to learn. We are also rehearsing a new song just written for this summer's Vacation Bible School Xtreme - we have to get it recorded in the next 3 weeks.
So why do I bring this up, I hear you asking? (I have a good imagination.) It points out the necessity to be flexible and good at what you do if you are going to be successful as a musician. The more skills you have - in my case this week, those skills include improv, good ear skills, ability to fake my way out of a musical jam (pun intended), and a facility with my ax of choice (keyboards, especially multiple keyboards).
Those skills, along with my ability to get along with people and my reputation for consistency and keeping my word - mean that the bands will hire me.
It isn't just the musical skills. It's also the people skills.
