micro motor mount?

Somebody explain why boger specifies a 12 degree bevel on the inner
and outer motor mount boards. My outboard has adjustible angle
presets built into it.....what is the point of the boards being
angled? I don't have a saw capable of cutting that 12 degree angle
in a 6 inch board in one cut, that's why i'm asking. In case it
matters my curent outboard is a honda bf2.
Thanks,
Jason