Why, when and where do we need lockout tagout?

When and where do we usually use these padlocks？Or in other words, why do we need lockout tagout, which is so-called the loto?
We need lockout tagout to guarantee safety in many dangerous places and areas, such as places with power switches, air supply switches, pipeline valves. Places need prominent warnings or authority management should be locked as well.
I summarize three conditions when loto is a necessity.
First of all, we need loto for the daily maintenance, adjustment, inspection and debugging of the machine and equipment.
Second, places with high voltage should be locked to guaranteen safety.
Thirdly, when the machine needs a temporary shutdown, we need loto to avoid injuries.
In a word, loto is essential in industrial operation. We should be aware that any step in the process of machine operation may cause accidents. To protect the people and avoid financial loss, we should try our best to avoid them.