One of the theories behind bias binding is: the threads of the binding are all running at a 45 rather than straight along the edge. This means that the edge of the quilt does not wear out along the edge as fast? I use bias if doing curves. On straight edges, I find that straight binding lays flatter with fewer waves.

I like a bias binding if I'm using striped fabric. It gives the stripes a diagonal look, and is more interesting. Otherwise, I only use bias binding if there are curves.

I make all my bias bindings..I have a binding machine that requires it...Its stronger that way but, if not using a machine like mine I think its a personal preference.

Same with plaids and ginghams. They look really nice when cut on the bias.

Having been a clothing and home dec sewer all my life before starting quilting a couple years ago, I made many many many yards of bias binding. You can get about 9 yards (roughly) of bias binding from a yard of 44" fabric. It makes a beautiful rounded corner which I love for some quilts. I made a silk quilt with a silk velvet backing and made bias of the silk velvet because mitering corners on bulky velvet would be very difficult, I rounded the corners and hand stitched the binding down; it came out beautifully. I had never done straight grain binding till I started quilting; still prefer the bias. You will find as many opinions as there are techniques.

I do not cut my bindings on the bias and have been quilting for 40 years. A straight grain cut is usually done.
A bias cut binding is only necessary on a scalloped edged quilt
where the binding needs to fit a rounded edge.

I agree!

If i'm using bias binding - i pin it to keep it from stretching as i sew - this may be why it's not laying flat.

I normally use straight grain because it's simpler. I do want to thank you ladies for this thread today, because i'm quilting a project that i'm going to curve the corners instead of squaring them off.

I learned that cutting on the bias for borders and bindings made the seam more difficult to see(?).

All my binding is bias cut. Probably because "that was how MaMa did it". I do find that I can finish my binding more smoothly with bias. My granddaughter only uses straight cut binding, and her quilts are always beautiful. I'd say to do it however it works best for you.