It might not be superuseful, but It can be good if you don't want to stand around for 10-5 minutes before WG starts.
Anyway, I joined the queue for WG ~11 minutes before it started, and then joined a WSG since I didn't just want to stand around.
When WG pop'd, I was able to join it while I was in combat, and I didn't get any deserter buff from leaving WSG. As I said, it's not superuseful, but now you'll atleast know that you don't have to stand around for several minutes before WG is about to begin, but you can actually do some BG's, and you'll be able to join anyway.