As the title suggests. Multiple times I've accidentially hit the side-key on my mouse that goes back in the browsing-history while typing a long post. Mainly while typing a long post, because I'll tend to take little breaks in between on the other monitor, and boom - everythings gone. A lot of other sites/applications would attempt to save the content of what you are currently typing in case this (or any other situation like browser/OS crashing, power-outage etc) happens, you can just continue where you left off.
Not sure how often this happens to other people and how much work it would be (I'm guessing the answer for the latter question is “a lot”). But just thought I'd throw it out there because I just totally don't want to type that thing again, and having to change my mouse or use an external editor doesn't seem like a good thing to me.