For fighting in opposite stances only; IE; one in southpaw one in natural ; If your jab is slipped and he moves to the outside of it ,you can keep it mostly extended and use it as a guard and a feeler by bodily turning into the direction they have moved to.
This allows you to regain contact ,distance and allows you time to set up your stance to his new position while remaining covered against his reply.

Its not something you would want to do everytime but it works when readjusting (maybe because space is limited through ropes or a ref) or if he hugs tight to your outside elbow for the overhand reply etc.
Leave it up and out ,turn in slightly and you have its path covered!