you might over do the grain crushing and end up with a lot of flour
The crush is exactly that: Squeezing the grains between two hard surfaces as opposed to grinding it between surfaces moving in opposing directions.
Something about wanting to keep the hulls as intact as possible.
Mind you I have never tried to brew with flour. It might work or it might just turn into a big lump of dough.
I'm betting on the lump of dough.