What is the origin of the idiom "dead man walking" and when to use it?

The phrase "dead man walking" originated in American prisons in the 20th century, where it was used to alert staff members that a death row inmate was being led to their execution. The phrase was reportedly first used in the 1980s by a corrections officer in Louisiana, and was later popularized by the 1995 movie "Dead Man Walking." The phrase has since been used more broadly to describe a person or group who is in imminent danger of facing a negative consequence or punishment, or who is likely to lose something of great value or importance to them.