By participating in the census you will increase the visibility of your derivative within Debian, provide Debian contributors with a contact point and a set of information that will make it easier for them to interact with your distribution.
For Main LinuxMint releases: Representatives of distributions derived from Ubuntu are encouraged to get their distribution added to the Ubuntu Derivative Team wiki page.
For LMDE release: By participating in the Debian derivatives front desk you can support other Debian derivatives, share your experience with other Debian derivatives and with Debian contributors and benefit from the experience of other Debian derivatives. Debian encourages representatives from all derivatives to join the mailing list and IRC channel. Future plans for the Debian derivatives census include keeping track of Debian derivatives, addition of more information useful to Debian contributors, inclusion of machine-readable information and subsequent integration of information about derivatives into Debian infrastructure.
http://www.debian.org/News/2011/20110124
http://wiki.debian.org/Derivatives/Census
** I can see that LinuxMint's LMDE release is already listed here.
