In System > Settings > Local Optional Features are two settings: Reconnect, and Save Open Windows. They both have the same three options:
System Default
Automatically
Never
I understand Automatically and Never, but where is the System Default set? I've had a look at the source code and can find no reference to those anywhere other than this screen.
Also, when Save Open Windows is set to Automatically, it can cause a problem in single user mode if the client crashes, because on reopening the client and logging in, it can fail to display any windows at all and only runs in the background. I've not found a way to recover from this problem.