I've changed how I run tabletop games over the past thirteen years. I used to define everything about the world, leaving the characters fairly constrained in an approach referred to by M. Joseph Young as trailblazing. My partner John has referred to trailblazing before as 'the tour bus'. The GM drives you to Plot Point 1, points out some stuff, and entertains the PCs with a canned scene while they act the peanut gallery and do their quirks/traits at each other. Sometimes there's a scripted fight. Then back onto the tour bus for the next destination.