The "point" or "nib" comes from sharpening a corner chisel on any stone (flat or wheel) that has a rounded left or right edge, instead of a sharp, square edge. If the stone's edge has a radius, then the corner chisel will end up with a nib.

(In fact, if you sharpened a straight chisel on a stone with a rounded edge and hung the chisel a bit over the stone's edge, it would also develop a nib on that side -- the nib is caused by overhanging a stone with a round edge, and is not a "corner chisel" thing.)

The nib brings no particular advantage--I have some corner chisels with nibs, and some without, and they seem to operate about the same.

I agree with Rudy about swept-back. The corner chisels that I use that have edges that are 90 degrees, or about 90, to their length, work well. Truth is, though, that I don't fret much about that angle--as long as the two edges are the same angle, not two different angles. The two edges must also be the same length, of course.

Corner chisels are great for chopping angled mortises (like knee braces) because corners chisels shear and split at the same time, unlike straight chisels.

Sharpening shops have a hard time sharpening easy stuff correctly. It's better to do corner chisels yourself.

Best
Robert