It puts the sights further away from the eye so small aiming errors are more obvious. It is not easy for most, but most can do it with practice and it becomes "natural" and "comfortable and "stable" over time. I was taught by a really good precision pistol shooter and his preferred stance was actually facing slightly away from the target, aiming by looking over his shoulder. He did not teach this and recognised that it was quirky, but it worked for him.

[Edit: This is of course only helpful for precision disciplines or where two handed grip is prohibited in competition]