I’ve only heard that it is only used by people in the same neighborhood to talk about people “who don’t belong there”.
It's actually quite useful for "hey, did you see my dog?" or "do you know what happened at ... last night?" things. But being a social network (so basically, evil by definition) you do get a worrying amount of "these people look weird here" , political fights and other BS that comes weith the social network territory.