Rejected conventional wisdom:
Imagine for a moment if the Grateful Dead had put themselves in the care of a manager who was focused on selling records and increasing the profi ts of a record company. If they had conformed to “industry best practices,” the Grateful Dead might be one of the thousands of bands on the dead heap of music history. The concert-as-business-model worked, and the Dead created a passionate fan base that became an underground cult that catapulted the Grateful Dead into the rock-and-roll stratosphere: the fan base grew from thousands to hundreds of thousands to millions, with the Grateful Dead selling out shows year after year.
So, in disregarding "concential wisdom" They
1. Didn't need to rehearse
2. encouraged people to come to many shows hoping they would see and hear something different. The friends in the crowd were just as important as the band and the music.