I will also try to add some things again to this page:
http://www.piratesahoy.net/wiki/new-horizon-modding/
about the stuff I added and how to used it. I tought I made an article already about how group dialogs etc worked but guess not.
Those functions can be interesting for quest writers, for example I dont know if you know yet but you can now assign multiple dialog files to one character and the game will merge them together (if they have the same note). So you can for example have a group dialog file for all citizens and give them personal special dialog files to add character specific things.