I like to use this method when making a baby quilt because they can't chew off the binding. But, it depends on if you are just self-binding or self blanket binding. Regular binding, you could leave 1" to 1 1/2" and fold over and bind. If you want more of a blanket edge, then leave your batting wider and leave the backing the width of the extra batting plus 3/4"" to turn under (this allows 1/2" turn under and an overlap of 1/4" to stitch down).