Importance of fabric grain in embroidery
I know the weave of the cloth makes a very big difference. 

I am a weaver and have seen professional looms in action. Grain, as I understand, is the Warp + Weft in threads per square mm, or inch. 

The grain is a living part of a fabric.  I would take that into accord, but I've not done a lot of "fine embrodery". It is just logical.