Saving Leases - explanation

Implications of saving leases in a database. What are the requirements for saving leases (when must they be written to disk)

What are the options for where to save the leases and the reasons for doing it one way vs another?

What are the implications of saving leases for: Latency - time used for this operation Database access - when will it be required, what is the overhead

requested by ISC support, in a KB or the ARM, thx