When working on an electrical circuit or device, always turn off the power before working on the given circuit to avoid electrical shock or damage to the electrical wiring or devices. Not only is it important to turn the power off, but it is equally important to test the circuit afterwards to be sure the circuit is really off with a circuit tester. There is always the possibilty that someone could come behind you and turn on the circuit that you are working on, unless you have the circuit marked with a warning label telling others not to energize this circuit or by having it locked out from use.
Electrical tape can be your frind when devices or boxes have exposed wires either connected to them or just hanging there unconnected. With the electrical circuit shut off, the circuit tested for safety, and insulated tools to expose the device or connection, it is now safe to disassemble the part of the circuit that needs inspecting.
