i never cut mine at bias

I cut mine on the stright. I don't do curves!! lol
simple quilter.

I always make mine on the bias. Way I was taught and am told the edges don't fray.

This may have already been said but I don't have the time to read all the posts so excuse if this is a duplicate answer. Binding cut on the straight of the grain has one or two threads
running down the outside fold. Thus, those couple of threads wear out. Look at antique or vintage quilts (most of which did not use bias binding) and you can see the binding still intact on the front and the back but usually very worn and shredded on the very edge. Bias binding distributes the threads on the edge of the binding, the threads are at an oblique angle to the cut edge, thus they don't wear out as evenly. Picture a piece of striped fabric cut so that it's on the grain with the stripes parallel to the cut edges, fold it in half. See how one stripe is running down the fold? That one thread (or stripe) is getting all the wear. Now, picture that striped fabric cut on the bias. See how the stripes are slanted from one cut edge to the other? Fold the edges together. See how no one stripe is getting all the wear? That's the wear issue. If the quilt is a wallhanging or something that is not going to get a lot of wear and washing, a straight of the grain binding will be fine.
The other issue is that bias binding is easier to use on curved edges, like scallops, because it has more give.
The other time I like to use bias binding is if I am using a striped fabric and I want the candy cane stripe look.

They do not have to be cut on the bias. The ONLY reason to cut a binding on the bias is when the edges are curved. Bias, as many believe, does not last longer than straight-of-grain. If the sides are staight, cut fabric on the straight-of-the-grain. Or down the length of the fabric. There are some times that you might want to emphasis the pattern and cut it on the bias when the quilt's edges are straight.

However, when only the corners are curved, but the sides are straight, I have pieced bias strips onto a straight strip in order to turn the corners without rippling or pulling. This takes some measuring though.

Sandy

I never have, nor many of my quilt circle.

Bias bindings have traditionally been used because the threads do not run parallel with the edge of the quilt. The wear is distributed among more threads and the binding will last longer. Bias is easier to use and gives better corners. Def a must if you are doing scalloped or curved borders or edges ie. Double Wedding Ring etc :)

I have ALWAYS done bias binding because I learned how to quilt in 1973 and that is what all the instructions said to do. I like a nice tight, trim binding and have gotten many compliments on my bindings from judges in quilt shows.