These are all good discussion points. I have been to jams where magic happened. It's elusive, though. Most people are not pure blues or pure anything, for that matter, Nic.
If a little common sense were applied to the general "rules" as proposed by Jim, we would have a wonderful situation where musicians could test the waters or get their feet wet. I've seen 2-3 guys work on something in the garage and then recruit a drummer or bassist or keys or guitar from the crowd and shine.
I've seen egomaniac players sing from one tune to the next without telling anybody in the jam band what key or tune they want to do next and then #@$@# onstage in front of the crowd about how the band sucked. I've unplugged 1-2 of those jackasses myself.
I've seen 5 guys stand onstage and nobody sings. Did you talk to one another before you got up there? Generally speaking if all involved are interested in presenting a finished product that's acceptable and they can communicate...NOT HACKS.
Anything else including daytrippers & egomaniacs (talented or not)...HACKS & WANKERS!
ALSO: There is a balance to be had if you're running the darn thing. You have some obligation to give all their chance in the order they signed up...not putting in your drinking buddy in ahead of all the jammers who've been patient is a good idea.
At the same time if somebody sucks there is no obligation to give them their 3 tunes. The crowd will tell you. But it takes work and you have to pay attentioon and be fearless. Most stage mgrs in the lower end just sit out back in the alley and get stoned.
The last point I'll make in this epistle to the sinners is that the higher the level of talent and musicology, the better and easier and more fun the jams are. I've participated in Jazz/Blues jams where there were Berk & Juli grads and there were no attitudes and it was simple...whomever sang lead, led the band.
They had no problems with egos. Conversely I've been in jams that almost erupted in fistfights because of misplaced egos and poor communications.
AND don't let a bassman or drummer tell a guitar wanker that the chord is a E7sharp9 not an Emin7. or that the turnaround in the Thrill is Gone is major even though the song is in Bminor...or what is 12/8 anyway?
PBBBBBT he says sticking tongue out, feeling feisty after bad day.
BJJ FDOL
Rock On & Keep the FAITH
It is
Blues From the Bottoms