It allows people to make others aware of news, happenings, and snarky/humorous comments.
It has little ability to inform or convey more than the simplest of information. It is a good way to alert and link to more indepth information.
It is nothing more than a network, and if you have your network set up like you want, it does a good job of letting you know when something happens.
But it is horrible for meaningful conversation, and more news than a standard headline. Thus you need to us it to link to a real news story.
I think this is what makes it that much more attractive to trolls - you don’t need more than a few sentences for drive by tirade.