I'm afraid I'm probably something of a misfit in almost any session I might sit in with. Spoilt by m' early trainin'.

There is a lot of jazz that I enjoy listening to, but it's not something I care to play much. Somewhere in the early sixties I encountered something of a "sequence" of several well known performers, in live performances, who all seemed to subscribe to the "ifIplayawholelotofnotesreallyfastandruneverythingtogetherandignoretherestofthebandeverybodywillknowI'mthestar" theory. People who had no idea what they were hearing would applaud vigorously, because they had heard that some d...d fool had concocted an esoteric "explanation" that this guy "had a new theory" and was doing something noone else had ever done - (sort of like a psychologist's after-the-fact essay on the "motivations" of a serial killer?). 'Way to intellectual for me.

I played quite a bit of "swing" and "big band" era stuff in a small dance combo for a few years, and it probably "stuck" my musical development to some extent. I like a good melody - which of course puts a lot of the more recent "pop" stuff out of bounds. There is some good stuff with complex (chord?) structure but virtually no melody - and it can be fun to get into; but there's a whole lot of stuff that's just "one-note-loud" and a heavy-handed rhythm.

There's a surprising amount of old "country" - '30s & on stuff we used to call "hillbilly," that's really good for melodic/harmony play. By any rational definition, this is probably the "folk" music some of us should be collecting today. It's (sometimes) good music. It represents what a lot of people liked about a generation ago, and to a degree reflects the culture then. It's not being played much anymore. And some of it, at least, is worth remembering.
I think it's been noted that "old-time" traditional sessions (barn dance style?), like the swing bands, played "harmony," and played together. When someone takes a lead, the rest of the group "plays around" their lead. If someone picks up the melody, I'd maybe play a mando "alto" harmony line on one pass and a "high tenor" above it for the next. Nobody plays "chunk-chunk" chords, except maybe as a rhythm fill.

In this style of playing, knowing what the chord is just tells you "which sandbox you're playing in." You make up the game - and while it's considered good form to "lead" to the next chord - or else be "in the chord" at the change, it can be a lot of fun occasionally to "lead" the group off track (gently, of course) just to see if they'll follow you, and if they can get back. (Sometimes you have to lead them back too, sometimes you have to figure out what kind of hole they're leading you into - and how to back up the "come-out;" and of course if the rest of the group doesn't follow you, you've got to come back without making an issue of it.)

A distinctly different style seems to me to be disgustingly popular. The whole group plays the same song all together. Then everybody goes "chunk -chunk" while the banjo player gets to be the star - all by him/herself. Then everybody goes "chunk-chunk" while the mando player gets to be the star - all by him/herself. Then everybody goes "chunk-chunk" while the fiddle gets to be the star - all alone. Then everybody goes "chunk-chunk" while the guitar gets to be the star - all alone.

If you're gonna "chunk-chunk" you've gotta be "in" the chord, and not movin' around it.

Done by professionals with well rehearsed routines, this can be good music. Done in a session of amateurs, it's just B.-.O.-.R.-.I.-.N.-.G. (to me) - especially since most of the players will know only one or two tunes well enough to take their "flash" lead, and will insist on playing them at every session - exactly the same way, at the same speed, no variations.

Additonally, the guitar player will want to play his/her version that "leaves out" the notes that are hard to play on the guitar. The fiddler will want the version that includes his/her "double-stop-fancy" thing. & … &.… on it goes.

Even Bill Monroe said "everybody tries to play it too fast." And, especially if you listen closely to his later recordings, even Bill left out a few notes (changed the tunes) to keep "the drive" in.

I enjoy listening to a number of the "professional" Bluegrass performers and groups. I enjoy playing quite a few of the common tunes - but they're too pretty in trad style to be ruined by my attempts to "Bluegrass" them. (A few of the Bluegrass versions are quite nice, played at a speed appropriate to the group instead of "as fast as the guy who knows it best can.") I don't care much for sitting in with the majority of amateur Blue(gr)ass sessions in my area, and frequently find "drop-ins" at sessions who want to change them into BG fests more than a little annoying - because it happens a lot around here. I do know a couple of groups I'd gladly sit with, and do the "chunk-chunk," just because they play well and are good listenin' - but it's not my favorite style.

As to theory, my current need is better understanding of lead/transition chord variants. I have all the theory I need for this at hand - I just need (want) to sit down and "practice it into" my playing a little better.

All of this is a little off the (current) point, but maybe it will suggest a new angle - or some new points.

John