What's behind your Appliqué?
 

How necessary is it for me to cut the fabric from under my large appliqué pieces? It seems like a bit if extra work but more than that, what if some day the appliqued piece comes loose? Lots of potential for fraying etc.

That's the exact reason I don't cut away behind mine. But I've never done real big applique pieces.

I don't cut from behind either.

I don't cut behind my appliqués pieces.

I think the reasoning behind cutting is so the quilt doesn't get too heavy. It could also be quilters of the past were frugal and trying to save every last scrap. I haven't done any truly large appliques. The only cuts I've made in back of the ones I've done was so I could stuff them for additional effect. I stitched up the cuts afterward. I wouldn't call it trapunto. My work is a little crude for that.
I've also seen arguments against cutting away the back fabric due to it can weaken the quilt. I don't know how much difference it makes but I tend not to trim out the backs.
Rodney

I do not cut

I made one quilt with a life size appliqué of a woman in silhouette. Had it been a needle turn, I would have cut the back away but it was fusible. I hope it remains fused and doesn't "buckle" up as there is very little quilting on the actual appliqué.

I use fusible but only about 1/4 inch around the fabric edge. I don't cut away the back fabric.

Usually if you are going to hand quilt your appliquéd quilt it would be easier if you cut away the backing as you layer your appliqué pieces. It's easier to keep your quilting stitches the same length if you don't have to struggle through a few layers of extra fabric.

I only cut away if there are A LOT of layers, and it has built up. But I also try to plan my applique to not stack things like that.