A lot of the regular Nestabilties shapes have both a small and a large set of the same shape. Owning both allows you to cut 1/8" bigger mat instead of the 1/4" bigger mat you get when you only own one set.
If there is only one set of the dies, like for most Label Nestabilities, I use the outside of the die to cut a 1/8" wider mat. To do that, I usually tape the image on a larger piece of coordinating cardstock, place the Nestabilities die back over the image layer and cut around the die with scissors. You can also trace around the Nestabilities die, then take off the die and cut on your traced lines.
I wrote a quick tutorial for that on my blog. You can find it in this post.