What is joan didion's purpose in on keeping a notebook?

Well there are a few purposes in that essay, but here goes. A notebook Didion argues is something that is an expression of a person's feeling at a time rather than that of a diary which is a recount of an event. She attempts to point out that all the random facts and scenes in her notebook are of no significance to her but of emotional significance to her at the time. A notebook is essentially personal and unique to yourself.