Judo pins are offensive techniques used to immobilize your opponent without causing him or seriously risking of causing him any bodily damage. Pins are rarely, if ever, used in self-defense as they require significant technical mastery as well as physical strength and, even more important, can’t be used in fight against multiple opponents.
In combat pins are serving the same function as joint locks as both used to control and limit movement of the opponent. The difference is that while joint locks primarily using threat of pain as means of control, pins limiting movement without causing pain.
Saying this doesn’t mean that pins have no practical applications, but just that those applications are not in self-defense. General Schwarzkopf used it in Vietnam to save his wounded soldier on a mine field, first responders and controllers in psychiatric institutions use it to subdue delusional unresponsive patients (who may be in pain or in aggressive shock), correctional officers may use it to subdue prisoners in some situations, etc.
From Judo pins to self-defense techniques