If I am doing large appliqués, I “ window” my wonderunder fusible. Windowing is when you just do about 1/4 inch fusible around the outside of the appliqués so the center stays soft and pliable in a quilt. If you are using something like misty fuse, you can use it under the whole appliqué because it stays soft.
If you are going to machine stitch a blanket stitch or similar around your appliqués to attach them to the background, I do recommend you use at least a fusible at the edge. The fusible helps to prevent fraying and adds a little body to the edge making it nicer to stitch on.