The pointy bit on a corner chisel is not intentionally created. It comes from sharpening the chisel on a stone that has an edge that is not a perfect 90-degree angle.
Take a look at most stones (even new ones) and you'll see that its long edges are a little rounded over. (Old stones are often very rounded, and that's probably why old corner chisel's have large nibs!)
A stone woth a rounded edge causes less steel to be removed from the part of the chisel that is closest to the edge of the stone (and more steel is removed from the chisel that is farther from the edge of the stone). Since less steel is removed at the inside corner than at the chisel's straight edge, a nib is produced.
Another way to visualize this is that the chisel simply becomes a mirror image of the shape of the stone that it is sharpened on.
The nib causes no particular harm, and probably has no substantial benefits either.
The two sharpened edges should be the same length, have the same angle, and the same bevel. But the edges do not really have to be 90 degrees to the length of the chisel--they could trail off somewhat without causing a problem in use.
My best
Robert
