As for the 'blend corner', it is not the classic blend, but it should be used on an existing blend, where it replaces the patches with a unique one, to make it aesthetically better.
What does aesthetically mean better?
Try to make a cube with 3 fittings that arrive on the edge. . .
Maybe different rays.
you will see that the closing "patch" will be of poor quality.. .
often, for moulding and aesthetic rendering reasons, we want to replace "locally" that geometry with a geometry that emphasizes the feeling of "curving".
I just have a second place 2 pictures to make you understand