The notion of a flat spot developing in the crankshaft is true if you let it sit for about a trillion years, of course by then the entire engine will be a flat spot… No truth to the notion.
Best to turn over the engine periodically just to keep the oil flowing.
I discovered yesterday why my intake valve was always out of adjustment when I checked the valves after our two week trip. The pushrod socket for the rocker adjustment screw has two 1/8" to 3/16" pieces of metal missing from the deep socket. At first I thought the slots in the pushrod socket were part of the desigen but on close examination, the metal showed signs of disintegration.
Because the intake valve was always out of adjustment even after adjusting the valve/rocker clearance, I suspect we purchased the problem when we bought the boat - it is life.
Fortunately, this is a simple problem to solve - $$$ for the pushrod and adjustment screw and 1 - 2 hr of my labor.