Brief Summary
This feature is for when you have a lot of open tabs, and you don't want to have to close then manually, so the browser would close tabs that have not been accessed for a certain amout of time.
Details:
A user would go to the settings page, change the default timer(could be 15 minutes) to what they choose, and as he leaves tabs open, the timer for that tab starts, and if the user did not access that tab before the timer runs out, the browser closes the tab.
Other options the user would have on the settings would be to select if pinned tabs, or tabs that are playing sound should have a timer. Also would be nice to set certain domains to not have a timer. All the tabs closed this way should go to the history like every other tab, so if the timer for a tab has run out you could go there to reopen the tab.
There's an extension that does this, but it doesn't work well with Orion, and I believe a "native" implementation would be more stable, scince they're not looking to make the extension compatible with webkit based browsers, so there's a good chance functionallity will break more in the future.