At the moment setting "close_windows_when_empty" results in the following behaviour that I found unexpected, and request be changed.
Set "close_windows_when_empty" to true.
Open 2 files in a sublime window. Drag one tab to a new window.
Drag that one tab from the next window back to the original window
The window now has no tabs or open folders, it should close.
It doesn't close.
Customer support service by UserEcho