What is the main purpose of a diary entry?

the main purpose of a diary entry is to record of what you did that day.

Updated answer

There are three distinct uses of a diary. The first is to record what you did each day, 2d it can also be used to make notes on future appointment, so that you don't forget them. Like a doctors appointment for example. 3d it can be kept with other diaries to become your personal history.

Ann Franks diaries are good example of how diaries are a personal record of a persons life. They are your intellectual property and can also contain fact and figures of important times in your personal life. If you have an eventful life you my use them to write a book.

Diaries are quite important.