Anything that spreads more music to more people is a good thing. It would be justice if the big labels let the market decide what to buy as opposed to dictating to the market that they must buy, e.g., Justin Timberlake (by paying clear channel to play it over and over and over and over...)
The only problem with jam is, like jazz, improve performances take up too much time on the airwaves. If stations make money by the adds, playing an extended cut = losing money.