These blocks act something like [event handlers](https://en.wikipedia.org/wiki/Event-driven_programming#Event_handlers). They send a run signal down their third wire in response to an event from an outside source (user input, or the physics engine).

Although they're somewhat like event handlers, they're still governed by the execution ordering rules. Basically, if their triggering event happened during this tick, then the block will send a run signal down its third wire when (or if) the block executes during this tick.