In lockout tagout, the main purpose of locking out an electrical circuit is to prevent electricity from powering certain machinery or equipment. Typically, this is because a particular machine has to be repaired or serviced. Stopping the flow of electricity to the machine keeps it from turning on and potentially harming the repair or maintenance personnel working on it.
Once any repair or maintenance work is done, employees have to follow a set of procedures to remove the locks they installed. This includes removing electrical circuit breaker locks, which can only be removed by the authorized employees who installed them.