When you have a team of people working on repairs to a power supply, you need to be sure that everyone is finished before you switch the power on again – the safety lockout provides a foolproof solution.
...see also our Socket-Pro range of protective covers for protecting individual 13a sockets, light switches, etc. They offer simple low cost protection against damage to or misuse of electrical power sockets, as well as protecting toddlers against electrocution, etc.