A pin rather than a toggle. I prefer to eliminate visual distractions whenever possible, and keystrokes whenever possible. When I click my document, 99% of the time it means I’m done with the sidebar, so it’d be cool if it auto-hid. And since unpinning triggers auto-hide, it would still work essentially the same for people who prefer the current version. Well I guess they’d have to repin each time. But serves them right for hiding it, they need to make up their mind.