I built my ballroom as a generic public lot, without requirements, tailoring instead toward assuring I offered facilities for meeting any requirements a grand ball might have as a scored event, e.g. a bar, from which one can get a drink, in addition to suitably housing a ballroom dance floor (medium or large required for the event - petite does not suffice) and then decorating lavishly.
Newcrest is my usual build world, so there it remains, and my sims are able to host grand ball events there.
If you also wish the same facility to support the functions of a noble court, then it also requires a podium for speeches a throne, and a fencing dummy or two (Royalty & Legacy), and must be placed on a lot in the world where your sims are nobles, in order for them to be able to fulfill all professional obligations there.