[sksksk]

This light is an at intersection, the other three roads leading to the intersection have traffic lights too.

If there is a power cut, then the other three roads will have no lights, drivers there will treat the intersection with one set of rules. Whereas the driver on this road with a sign will treat the intersection with another, potentially causing an accident.

[lisper]

There is no more possibility of an accident with a stop sign than with an always-red light because the rules for both are exactly the same: stop, and proceed only when there is no conflicting traffic.