If you make in the alleged Cremonese methods, then corner blocks are needed. It seems quite clear the that Brescians didn't need them. If you use an outside mould, or build on the back, you don't need them. If you were Flemish, you set the ribs into a groove in the back, so no blocks needed.
Mostly for glueing surface area, I would guess, unless you are using the inside mould and need them for the shape.