I use it primarily for gravity training, but it can be used for isometric work as well. I would never use it only for isometric exercises though. It has to be used for a variety of exercises to be effective. It’s just like only performing isometric exercise does very little for an athlete anyways.
You can use the elbow limitation while performing isometric exercises with a closet pole. By reducing movement, you shock your muscles into working even harder to try and break yourself out of the predicament. It could be a psychological fear of being tied up or in a tight space. You want to break free from it and will work harder to get out.
Slaves tend to fight the hardest to be free rather than the free fight hard to be more free. In a way, you need that psychological and physical disadvantage and limitation so that you can become even better at what you do.