I have seen this in many famous fashion shoots done outside. Something like this picture below:
So does the model stand in front of it as backdrop? then wouldn't it block the background view in outdoors? How do they use it ?
I can think of several ways you could use it...
backdrop: If the creative directory wants two looks with the same model in the same clothes, shooting both at the same time could save some time. Just because you're on a beach doesn't mean that every shot has to include the beach.
lighting modifier: Shooting with the screen out of view but close to the model could add some direction to the light. In the shot you posted, the sky is overcast and the light would be coming from all directions; blocking the light on one side would give the shot some dimension.
privacy screen: Two or three of those screens arranged together could give the models a bit of hidden space for changing.