The idea: Extend the date range in date and time-stamp fields, functions and layouts (date picker) to include BC years. It is important to have the option to include a year zero or not.
FMP already serves the interest of historians, archeologist, linguists and astronomers and other people with an interest in the past, by supporting dates going back to 1 January 0001. However, the omission of BC years cripples that effort significantly.
The option to include a zero year or not, expands the width of potential interest. Astronomers work with a zero year, whereas scholars in the humanities work without a zero year.
For further background see the thread Wish list for extended calendar support