Aditya Athalye has a nice post on how he uses Org-mode for writing and more. Like most Org users he started using it for a single task and discovered, as he went along, that he could also use it for other tasks.
Like me, his main use is writing. He writes his blog, his talks and most everything else in Org. As I’ve said many times before, I hate writing in anything else. The thing about Org—when run natively in Emacs—is that you get all the advantages of Org markup along with the superior editing environment provided by Emacs. I would use Org even without Emacs but I wouldn’t enjoy it nearly as much.
As Perry Metzger recently said in an Irreal comment, Emacs really does provide a superior editing environment that makes editing text much easier than in other editors. If your priority is efficient text entry and editing rather than bling, it’s a no-brainer. Take a look at Metzger’s comment for one of many reasons why.
Athalye considers, among other things, why you should use Org markup instead of Markdown. Both are way better than the WYSIWYG editors but Org is I think the better alternative. Karl Voit agrees. One of the main ways that it’s better is Babel and the way it enables “live documents” that rewrite themselves when the data they describe changes.
Another advantage is that’s there’s only one Org whereas there are several flavors of Markdown. This is mainly due to the tight coupling of Org markup with Emacs and could change if Org markup obtains enough traction in other editors. That’s why Voit, at the above link, argues for a standardized Org markup that’s the same with every editor.
If you want to see some good reasons for why the effort of learning Org is worthwhile, take a look at Athalye’s post.