How have I not noticed this before?!? Thank you! Wow this makes it so much easier!
I'm not sure this was always a thing we could do; I seem to remember people preferring to teleport in from an adjacent area in 3.0 just to be able to zone into the right instance for hunts and the like.

Then again, if it WAS always a thing, there's probably a crap ton of other people who are just now discovering it and are probably feeling stupid too.