No reason why you shouldn't use the back. Only I would be careful mixing front and back in some cases.

I made a project that was just a gift. It was really my first attempt at making a quilt. but to me, a quilt is not a quilt without batting in the middle. Back then, I didn't know what batting was. Anyway, I used the back of fabric one time. I needed a pale piece of fabric and the red I had was just too dark. So I flipped it over and it was just fine. The name of the project was "From Sea to Shining Sea.". So, I think it's ok to use the back of the fabric every once in a while. There's no real rules when it comes to quilting.

Let me check the law book. Uh....no problem!

sandy

I recently took a class where the instructor encouraged us to use the "wrong side" to give a lighter contrast to the fabric in the pattern... before that, I hadn't given it any thought.

Back in the day when I was doing theatrical costuming, I often used the back of the fabric because it had a nicer texture than the front. When I am piecing a quilt now, I look at the fronts and backs of my fabric to see which one gives the effect that I am seeking. I think that in the present almost anything goes with quilting. We are not limited to just 100% cotton fabrics, so why limit yourself to using only the front?

A couple of years ago we were given an ugly fabric FQ to use as an officers challenge. The back was a pretty greenish color. We had to use at least half of it in our project. I made a wall hanging using it and used mostly the back. At first they said I did't have enough of the ugly fabric in my project. Then I won first place for my project, partly for finding a unique way to use it.
Remember the only restriction on your projects is what your imagination can come up with. DO what you want, there aren't any rules! Use different things, it is how new ideas are created. Break the rules!

Many times I am given scraps that others are throwing away. Sometimes there are pieces that have metallic parts. Since that just doesn't go with a scrappy quilt (unless I would have a huge amount of it), I use the back side of that.

The "right side" is the side you like the best!

I also use the backs all the time! Some times I use both the back and the front in the same pattern when I want a "lighter" color that matches - in fact I'm doing that on the quilt I'm making right now!

Sometimes the wrong side is the very shade I am looking for. I use it and you know what? No one knows but me.