Within twenty minutes he went from not rolling over to rolling over quickly and constantly. Similarly, within a short window he went from ::wobble left, tip over right, wobble left, wobble right, tip over left:: to just sitting with the occasional backwards fall.
With both of the boys, the milestone of sitting brought big changes. Some physical discomfort dissipates as he can sit more comfortably and with a better view of his surroundings.
Sabien enjoys sitting with something to chew on and watching Wesley and me play on the floor. He can choose to lean over in order to reach something, and if he topples, he can roll over onto his tummy. In this way, he has much more control over his environment, and it's easy to see the development of his sense of agency. "If I roll, I bet I can reach that toy", etc.
While he's happy to scoot on the bed, he doesn't inchworm on the floor. For now, he's sitting pretty.