Facebook supplies a directory of everything happening in my city, algorithmically curated against things Facebook thinks I will like and which my friends have said they're interested in attending. It lets me organise my own events, and communicate easily with attendees, who can see which of their friends are attending and make plans. It lets me make contact with people I briefly met in person but wouldn't have grabbed their phone number/wouldn't text them out of the blue yet (because who does that?).