I am on a fairly RAM constrained workstation (4GB) so I have no choice but to close it when I'm not using it. Otherwise I'll spend just as long swapping as I would opening a new instance.
The biggest consumer of RAM for me is chrome, not windows, and it is basically essential to my development process to have it open all the time. So I worry an OS change would not produce an appreciable enough performance improvement to justify changing my whole workflow over.