It’s to aid in tight corners, instead of backing out and making a wider sweep to get in tight you can back the Saw into new material, kind of dumb if you ask me and can really do more harm than good if they aren’t used correctly. As for the double edged recip blades, I’ve never really ran into a spot demoing I wish I had an edge in both sides of the blade. The only thing Spyder makes that I would pick up are their hole saws!pretty innovative arbor Sent from my iPad using Tapatalk