Refers to where you hastily "make like a crab" when ambling along the road or down a long aisle/hallway and observe someone warily approaching with an extra-wide/bulky "item in tow", such as if a person is wheezingly lugging one or more large humongously-bulging sacks/bundles in his arms, or if a vehicle is pulling an extra-wide trailer; the "courtesy" notation implies that you intentionally move aside considerably farther than is actually necessary for safely allowing the person to get by you; your purpose is to ensure that the trepidatious cargo-transporter can feel totally confident and non-apprehensive about passing by your position.
I always make sure to perform the courtesy-sidestep whenever I see someone approaching who needs extra room to pass, especially if there is a wall, line of parked vehicles, or other currently-immovable object at the side of the road that the person is having to actively avoid. And I also find that I can acceptably do so even if there are other folks present beside the road, as well... even if several people are also standing next to the wall --- like a bunch of huge burly D.O.T. guys at a road-repair-construction site --- I have never been griped at for just unceremoniously squinching myself right up against/among them till the extra-bulky vehicle has passed; I guess it's kinda understood that personal space/boundaries get temporarily "collapsed" or "suspended" when safety is at stake.
by QuacksO August 19, 2018