Er, sorry, Joe, I typed that before I read your excellent link, so I was sort of giving an unintentional potted repeat of a lot of its content...

I'm absolutely no lover of jazz, but we once took my elderly father-in-law to a Humphrey Lyttelton concert for a birthday treat, and we were subjected several times to that applause after solos within longer pieces. I must confess that I found that to be intensely annoying, seemingly to me more of an automatic in-crowd thing than true appreciation, but I'm more than happy to be shot down for expressing that attitude...