Welcome. I am new on here also. The folks here are a wonderful group, incredible resource, and funny too.
Oh this is a "chicken or the egg" question.
I pre-wash all my fabrics to make sure any "sizing" is removed before I use it in a project. This also makes sure there will not be any bleeding of color, but you are right that some fabrics will fray.
If you want to wash and avoid some of the fraying - baste the edges before you wash.