I like the idea of this being a configuration option, but not a mandatory feature. I can see the pros of it. Your presence on the servers takes up bandwidth, server processing time, etc. But at the same time, it wouldn't really save any power on your end as you'd only be logged back to the character select screen, which still requires the GPU's rendering power. It'd also be inconvenient should you need to go away for a moment (there's a large number of reasons for that, not the least of which is our own bodies) while partying. If you have the game close altogether, which would save maybe a little power, that introduces a whole other set of issues, including using the security tokens more hastening their eventual end.