What is the benefit of an atherectomy over an angioplasty?

Atherectomy v balloo: typically blocked arteries can be opened more widely by inflating a balloon inside the vessel. The balloon is then deflated and removed from the vessels. At times, heavy calcium makes the arteries so hard they won't open w/ the balloon. Some of those lesions can be addressed w/ Atherectomy, a device that shaves the plaque down creating a more wide flow channel.