Alright, this just happened to me, I was flying on a flight path when a warlock summoned me into an instance, but the instance was full, so it dismounted my flight path wyvern and put me on the ground. Hope this isnt a repost, Thanks.
This would be useful in Azeroth, not so much Outland
The full instance i got summoned into was a group where they just ditched the tank and he hadnt run out yet. Hope this helps.