Here a flyer has zoomed onto the board from a short table edge. His enemy has convienently left a tasty decoy unit for him to shoot. The blue boxes represent some terrain that it would be hard to put the flyer on, but due to flyer rules and the wobbly model syndrome rule, they are irrelevent unless occupied.
For his next turn, assuming the flyer wants to zoom, he must move within the green zone. If there is no place to put the base due to enemy and friendly models, there are two choices as I read the rules. The fly can't move 18" and is wrecked. (Yay!) or if the flyer has the Hover type also, he can slow down and act like a skimmer. (Yay!)
If you manage to immobilize a zooming flyer with a lucky shot, he has to stay at the same speed moving 18" or 18.1"-36" and can't go into hover mode.
I can see this maybe being used in the mid game by tyranids or other armies with a large footprint.