"When you fog the engine while
"When you fog the engine while it is running, the oil is drawn through the crankcase or intake manifold, into the cylinders, burns up (that is where the smoke comes from), and out the exhaust.
This leaves behind a nice thick coating of carbon on the rings and pistons, and very little oil in the crank or manifold.
If your goal is to make smoke and gum up your piston rings, then go ahead and fog while running.
It makes much more sense to fog while cranking. You use much less fogging oil, everything gets a good soaking with oil, and there is no carbon left behind by the burning oil, which can be especially harmful to a 4-stroke engine. It is not a bad idea to flush out the oil before starting in the spring for the same reason.
I have been using this method for only about thirty years, and have never had a problem, or a complaint from a customer.
In my opinion, the instructions on the can of fogging oil have only one purpose; sell more fogging oil.
Tony"