We need this feature! I'm not sure why it was deferred, because this seems like a big productivity plus.
As explained in the other answers here, such a feature should be similar in functionality to how Gmail works with drafts - if I'm drafting an email, it auto-saves, and then I can wait before sending it.
When writing a question or an answer, such functionality would have multiple benefits:
- Prevents data loss from crashes - let's say that I'm writing a question and I want to paste in some sample code, so I go into my IDE, with Stack Overflow open in a browser window/tab, and boom! My computer/browser crashes. All the question data I was just writing is lost.
- Switch computers while writing - I often get ideas for questions right before I have to leave somewhere (I have no idea why this is, though). This means that I either have to quickly write my question, thus delaying my trip and affecting the quality of the question. As Gmail allows, I want to be able to start writing a question (or at least write the title and a few lines of notes/ideas), save it, and continue writing it from another location.
If such a feature is implemented, it should apply to both questions and answers. While it would be more useful for questions, the first reason I stated above applies to answers, too. However, questions don't really have a specific time cycle (nothing will change if you don't ask the question right now, but instead, ask it tomorrow), while with answers, the original question and its answers will probably change. Who knows, maybe a great answer will have been accepted already, but the draft feature is still necessary.
On another note, I'm not sure we would need to purge drafts, well, maybe rarely (once every year would eliminate any problems with this), but we can discuss this later.
Such a feature would be awesome. Wouldn't you want your question/answer to be auto-saved while you're writing it?