Access to any areas that belong to endwalker content
Endwalker jobs
leveling past 80

skills and system will be updated to endwalker state for everyone
anything that's not BoP will be attainable so glamour, new furnishings and whatnot can be used
usually a decent amount of little new things scattered about in pre-existing areas

basically if your not 80 yet, absolutely no need to do it until you hit 80 and decide you want to keep going