Uses
Some system programs that never terminate execute an event loop, going to sleep at the start of each cycle and waiting for some event to awaken them. Once an event is received, the program services the event, then returns to the beginning of the next wait cycle.
Other programs periodically poll for events by going to sleep and resuming execution after a specific interval of time. Once execution is resumed, the program polls for events or status changes, and then services any that occurred while it was asleep. After servicing the events, the program then goes to sleep again for the next time interval. Certain kinds of heartbeat events or keep-alive signals can be generated by these kinds of programs.
Read more about this topic: Sleep (operating System)