A Dissenting Viewpoint
While there has been a lot of talk about the musical side of "big band" versus a smaller group, the main question in my mind has always been not about the full and lush harmonies (which I enjoy as much as the next person) but rather about the economic side of things.
Popular music has descended (if that is the correct term) from the expectations of art music (with dozens of performers) down to the "big band" (which comes in a variety of flavors, minus the occasional sax, trombone or two, and trumpet), through smaller groups, all the way down to the instrumentation made popular by the rock era: lead guitar, possibly a rhythm guitar/vocalist slot, electric bass, drums and a keyboard. This has been played around with over the years (with a single sax, or three horns, or some other variation), but that's what you see with "popular" music, and that's what people are willing to pay for, whether we like it or not.
Since opening up a six horn group (alto, tenor, baritone (all double on something else), two trumpets (doubling on fluegelhorns), trombone (doubling on rhythm and vocals), "the combo" (upright/electric bass, guitar, percussion and keyboards) plus vocalists, I've seen bookings pick up substantially. The payroll alone tells the story: thirteen shares for the six horn, versus twenty for the "big band". Talking better harmonies and the like is all well and good, but a forty per cent discount speaks louder than any nice music talk.
I prefer the full group (which we call a "Vegas style revue band", this to get away from the "big band" stigma that has now become almost all encompassing). But, I'm not the one footing the bills here - i.e., the client (regardless of being right or wrong) is always right. (I'll pitch a big band to a specific group, looking for the Forties experience, but limit music from that era in most other settings.)
Once again, it's not that I don't like the stuff from the Twenties through the Fifties - my group can still do a knockout version of Boo, Hoo, for example. It's just that the audience for most of that stuff has shuffled off the mortal coil at this point. There'll always be an audience for such classics as In The Mood and the like, and they need to be there in one form or another, but the days of crowding the bandstand with your sweetheart, Cokes in hand, wanting to hear 720 In The Books are gone now.
Incidentally, I've noticed a fall off in interest for stuff from the Fifties, including much of The King's oeuvre. This is sad, since for the small group I've got tons of Presley's greatest hits, but those folks are passing from the scene as well. (My lovely wife, a rabid Elvis fan, is seventy five, and many of his other key-tossing fanatics are older still.)
When doing retirement home stuff (I hesitate to call them nursing homes, since there are a lot of active retirement communities, all of which are loose with the money when it comes to their entertainment), I have even noticed a diminished call for stuff from the Sixties and Seventies. On these jobs, I always made it a point to take the whole book so as to be able to do requests, but for the last four or five I've just loaded up some of the salient tunes from the past into a special "fifth set" folder, just in case. And, it's seldom that those charts get dipped into. In fact, we get more call for waltzes than we do for Swing Era classics.
And, I know youse guys and gals like jazz a lot. But, with the exception of some classics during the cocktail hours (I do (or, should I say, did - the baritone hasn't been out of the box for about six months now) a great rendition of Basie's Misty, and there are a few others), we generally stick to four to the bar stuff that people remember.
Of course, there are "jazz bands" and "stage bands" that present the classics all of the time. But, they're not usually the ones people are willing to pay to hear, unless they have A Famous Name From The Past® fronting them (or at least on the music stand). And, even there, what's being presented is a ghost from the past.