Originally Posted by method
I think the advantages lie in a (typically) longer sight radius, and the fact that our eyes have the ability to find the center of a circle automatically. There's no thinking or effort involved in attaining a sight picture with an aperture rear, it just happens.
Plus there is no switching the focus between the front and rear sight. This alone makes them faster than traditional leaf or buckhorn sights.
I put a Williams 5D aperture sight on my Winchester 94 30-30. Out to 100 yards it is the equal of a scope and it is more robust and faster to use.