Business Events in Concurrent Program Definitions

In r12.1.3  we have following business events when defining a concurrent program using Application developer or system administration responsibility

1. Request Submitted
2. Request on Hold
3. Request Resumed
4. Request Running
5. Program Completed
6. Post Processing Started
7. Post Processing Ended
8. Request Completed.

Question:

What is the significance of above business events and how can we use it? Is there a documentation outlining each one of above events in detail?  Is there any working example?

Please advise.

Thanks,
Darsh