Twitter is very different to other social networks out there and works entirely different too. It's actually hard to explain what Twitter is to someone who's never used it before.
Twitter though has become a great way to share short pieces of info very quickly. Many business and probably every news publication in the world uses Twitter to share information, it's one of the quickest ways to do so to a mass amount of people.
Facebook isn't anywhere near as effective. If you run a number of Facebook pages, you'll see from the insights which sit below posts, that they do not reach all of your fans - they only reach usually a third or less. So sharing breaking news through Facebook is a big no-no. With Twitter, all your tweets go into all of your followers timelines, making it a lot more effective.
The infographic below goes through some very great facts on what are the best and worst types of tweets. They usually apply to everyone.