1. without a rapid shutdown device , there is no safe way to turn off the current running through those conductors
2. most people would assume that simply turning the solar inverter off would turn the power off, but it doesn't work like that. You would still have power being generated by the solar panel and you would still have power in the electrical cables coming from the solar panels.
3. this live current poses and electrocution risk to anyone who comes into contact with the solar panel system, including first responders who may be responding to an emergency on your roof
4. firefighters are at particular risk since it's common for them to ventilate burning structures by cutting holes into the roofs or walls, which may bring them into direct contact with the solar panel system's conductors or wires
5. solar rapid shutdown solves this problem by de-energizing the solar panel system in under a minute，remove the electrocution risk for anyone going on the roof