Why is it important to use diary systems to plan and co-ordinate activities and resources? Why is it important to obtain relevent information about requested diary entries and changes, and how should you solve the types of problems that may occur when new requests are made?

Just provided a long answer to one of the other questions. Read that and then think about it - it will lead you to the answers of all the other questions you've asked. It's just common sense really, you just need to think a little more about it and you'll see that all your questions overlap.