A rather unremarkable effect of atmospheric cooling occuring mostly in mountainous areas. As the ground cools, cold air has a tendency to flow down the sides of mountains. Not generally considered an issue unless flying with an overloaded or marginal performance aircraft at a high density altitude close to mountain slopes.
Wind rotor effects off the top of mountain ridges are by far the most dangerous weather effect close to mountains with vertical down drafts reaching several thousand feet per minute. Subsidence effects by contrast are measured at only two or three hundred feet per minute.
So for all practical purposes it can be ignored. There are far more serious hazards around when flying in mountainous areas.