Does he do this to cement Ash's superiority over the primitives, kind of like a medieval travelling salesman giving the patter and winning them over like a showman. Or perhaps to set up the final scene back in S-Mart....Hail to the King Baby! To be honest, I clearly have no idea, but thanks for the reminder to watch this again!

Or maybe it is just to relax the viewer ready for the shock of the Boomstick - lulling us into a false sense of security with the comedy.

Pacing. On the page, the dialogue would have been too long and slowed the read. In the movie, the camera keeps moving and the audience is allowed to drink up the scene until the hero moment. In any case, these guys were really in the zone. If I remember right, this was playing against FFC's Dracula when I saw it. AOD had way more boom the buck.