I was taught to use only cotton in my quilts and sew using only cotton. Quilting had to be done with cotton also, and only 50 wt. And stitch length had to be 2.5.
I saw some Leah Day videos and thought she had committed blasphemy...I was shocked to find out that other fabrics and threads could be used. I think I held my breath the whole time I pieced and quilted a quilt using Polyester thread. The world did not stop, caverns didn't open under my house and swallow me whole. And the quilting police didn't come and chain me to the bathroom sink. Now I piece with whatever thread I grab (although I admit to being an Aurifil fan), and I quilt with Aurifil, Isacord or other Poly threads I have in my stash. I caught myself wondering if using Poly threads would lessen the shrinkage of a quit when it was first washed.....nope, not for me.
I also have a ball trying to figure out which batting I want for a particular quit......so many choices.