I was just asked a very interesting question on Twitter: How is Twitter an effective writing tool?
My initial reaction was: It's not! I believe there are a number of great books that have not been written because their authors were playing on Twitter and other social media platforms instead of writing.
But that isn't the whole story.
Modern day writing is marketing and networking and so much more than writing. Tools like Twitter can be used to connect with other writers, agents, editors, and more. Twitter is like having a writer's conference at your fingertips whenever you need it.
Search on the hashtag #writing or #amwriting to connect with writers. Ask questions like this one. I'm guessing you'll get a variety of answers.
Connect up with other writers via #ww and ask them to hold you accountable for meeting your writing goals.
Also, use it to make connections with readers, so that when you are done with the book, you will already have a tribe who will help you market the book.
Unless you're writing one of the ultra-modern novels-by-tweet, I suspect a word processor or Liquid Story Binder (#LSBXE) may be a better TOOL for actually writing.