Answer Description
Redundancy is used to ensure if one device fails, a backup can take its place. Without redundancy, single points of failure can cause system wide outages.
Wikipedia
A single point of failure (SPOF) is a part of a system that, if it fails, will stop the entire system from working SPOFs are undesirable in any system with a goal of high availability or reliability, be it a business practice, software application, or other industrial system
Single point of failure - Wikipedia, the free encyclopedia