The idea of the friends system is to know where your friends are, if they are online, etc. It's for a huge group of people to interact online.
The party system is different, it allows a group of 2-6 friends to join up together and be able to have fun without having to message everyone individually, and execute multiple commands just to see where they are, message, and connect.
A party system doesn't have friends. Every time you log on you do /party add <name>, and you add the people you want to play with. Parties are to group up together and have fun. The friends system is to know if they are online and where.
Personally, I do not believe HHGN needs this at the moment.