There are no hard and fast rules about it. Some people don't want any quilting on the applique, others want detail quilted. Some times a lot of quilting is required on it. For example on this quilt the maker didn't sew any of the pieces down, it was all raw edge fusible (misty fuse) on un prewashed fabric. So the applique was coming up like crazy. the factory sizing kept it from forming a bond. I had to quilt the bejeebers out of it to get it to stay put and it was still coming up along the edges.
http://www.quiltingboard.com/picture...g-t256886.html . On quilts where the fusible has been secured with additional stitching I tend to just outline. But really there are no rules. Do what you think looks best and what you like.