If you're like me and spend your motes on exotic engrams whenever you can, you probably ran out of motes mid-reforging at one time or another. If you can't get your motes together in time for the end of the Iron Banner and/or can't get a good roll at the moment, you could end up with a weapon that you can't really invest in until the next Iron Banner. Why can't Gunsmith have this feature? It would be easy to add.