I've observed in usability testing sessions that there are many users (especially beginners) that forgot to save the changes they do.
- when they create the page, write some text and then get distracted by something else and leave the page without saving - see
- or they edit and don't find a functionality they need so they change the editor without saving - see
- or when editing the Dashboard and playing with the gadgets, coming back the changes are lost - see XWIKI-6150
- or when someone accidently clicks a wrong control element in xwiki, then all changes are gone (see attachment 'xwiki_dangerous_button.png')
Although displaying a non-intrusive message don't solve the problem (some user might see it others will not) at least it will be an indicator that there was something more to be done and the user will learn we needs to save.
Using a notification gadget will be better than an intrusive dialog box.
Knowing if there are changes and saving just in this case could also improve versioning, see XWIKI-2470.