I certainly believe that playing along with others will advance learners quickly. Not neccessarily with "advanced" players as all too often what's happening will be beyond them and may intimidate a nervous beginner.There's plenty of intermediate level players around who enjoy the chance to swap ideas and help others along. I've been playing for 30 years and try never to turn down the chance to busk/jam/playalong with anybody especially when they're better than me.