I started the topic because I saw lots of people think that they have to click on Preview button to save their posts in Draft page. Then, I discovered theymos announcement about Draft page long time ago, that clearly states that users don't have to do this, clicking on Preview button is just one of triggers for Draft page.
The other trigger is to actually try to post something. Your data could still get lost if your connection to the forum/internet is dropped, eg if you have a poor internet connection.