A solo cocktail piano player has a bit of freedom when using a fake book. He can get into and out of the piece any way that sounds good, take extra repeats, leave out the bridge, pick any convenient key. In a band, everybody has to know what’s going to happen.
I mentioned before that someone can call out an arrangement in a few seconds with some standard terms. A band that rehearses frequently and has been playing together for a long time will have a custom standard arrangement, and they won’t even need to say anything beyond that. While there isn’t a standard standard that all jams use, usually it’s close enough that I can roll with it.
In the trio, the intro is piano through the head, sax melody on the head, trumpet solo, piano solo, optional sax solo, and one or both horns on the foot. In the quintet, we usually start with the last eight or sixteen bars, have the horns split the head AA / BA or some other sensible way, do solos in order (trumpet, piano, sax, bass, optional fours with drums), horns split the foot the same way or reversed, and do one of our standard endings. In the vocal swing group, intro is either last eight or just solo piano, followed by vocal doing all verses, trumpet solo, vocal on last verse (or full head), end in a rallentando.
Endings are the devil. Sometimes the quintet does a rehearsal of nothing but intros and endings. We have perhaps half a dozen standards endings. In college pep band, the director had hand signals for frequently used pieces (for example, the fight song). So in the quintet, Bill can hold up two fingers, and we know to repeat the 3rd and 4th bars from the end up a step; or hold up three fingers, and we’ll do the Basie stinger.
With that, we can sightread anything off a lead sheet and know we’ll start and end together.