The only times I double stitch are if I hand piece and discover I've made stitches larger than intended, if my fabric is fraying (satin for instance), or if I get my 1/4" too scant when machine piecing. I try to always check seams as I press so I can redo if needed.
When I was a beginning quilter I used some fabrics that frayed badly in addition to having seams too narrow and had to do repairs which I would just as soon avoid ahead of time. I'm more careful now!