It has happened far too many times in my browsing experience where I will be typing a long winded form post and have lost the contents of the form.
This can happen by clicking a navigation link that takes you away from the page without realizing it would happen. When this occurs I would typically hit the back button and all the fields will be blank.

This situation can also happen where filling the form takes longer than the session timeout of the website. The website then informs the user they need to login again, and when they do the form contents are empty after the refresh.

Similar to the form auto complete for fields such as name, address, phone number, etc, a function to restore last filled values on the form, maybe by right clicking a field would be fantastic.