Back in the day (well Susan got to talk like a con, I figured I would stray a little bitt too).
Any way... When my friends and I would do "pig pick'ns' we would always mop. That's just what you did. That's what the NC BBQ joints did. Of course we were cooking a whole or half pig over wood embers (direct heat) either in a cooker made from a fuel oil tank, or a pit dug in the ground. The only rub we used back then was salt. You salted the pig, thru it on the grate, drank beer, tended the fire, and mopped your pig with 'dip'. 'Dip' is what the mop sauce is called in Lexington (BBQ Capital of the World) and surrounding regions of NC.
Using my WSM I'm not as prone to do it. Don't want to lose the heat. If I am opening the lid for something else I will mop.
And yes, one day before I die... I've got to party with Susan.