Who can access this data? I think that only administrators have access to such data.
I can confirm that users don't have to click on Preview button to save draft version of their posts.
Please don't make me laugh if you actually don't know that page.
Everyone can see their draft pages through the link (after log-in):
https://bitcointalk.org/index.php?action=draftsI think you need to either click to post or preview in order to save draft. The forum does not do this automatically.
You can also extend the duration and add a link to the topic through some source user scripts.
I don't check about PMs, but for posts, I checked it myself. I created the thread, just to checked it will be saved in draft page without clicking on Preview button or not. Result is without Preview button click, Draft page saved it. You can check it with your next post.
Honestly, I read other people said that clicking on Preview button is mandatory thing to have saved posts in draft page, but it is incorrect, from what theymos wrote and from my experience.
I think that this draft page is almost useless the way it is.
Auto deletion after 7 days, lack of manual deletion, and so on. We are all basically forced to use a third party editor, even having a native draft page here.
I created a topic about it in meta with suggestions of improvement, but nobody seemed to care, the answers were like "just use an external editor"....
But it at least can help if you delete your posts, and want to get it back within 7 days. As I wrote in OP, for important content, it is always better to compose, edit, save in external text editor. Draft page only should be used in the case we don't save texts in external text editors.
In reality, I think most of us rarely use draft page, and it is one of reasons why draft page has not yet been upgraded. Mainly due to lack of interests, and real usecases.