That last part is really the reason I chose this image for today's post:
Communication is only really communication if you can't predict what will be said.
Yes, when a child requests a favorite toy using symbols instead of throwing a fit, that's HUGE. But we can't exactly say that it's unpredictable that a child wants their favorite toy. True communication happens when that child says something we would have never guessed -- something that surprises us. Something that's entirely from them.
It can take awhile (and a lot of aided language input) to get to the point where this happens, but in my experience it's well worth the wait (and the effort).