I'd been working on a lengthy post that involved quite a bit of time and research. I saved now and again, but when I clicked Save to backup the final draft before proofing, I received a message to the effect that I did not have the rights to do that.
The post vanished and I had to log in again. I opened the draft of the post and half of it has gone because neither the auto-saves or manual saves had worked as the system had logged me out halfway through.
There should be a better way of handling an automatic log-out than this. It's infuriating to loss a substantial part of a carefully researched and considered post because the system decides it's time to kick you off.