Isostatic stretches is a flexibility exercise, it can be important because you need to have flexibility in your body but it can also be dangerous very dangerous. It can damage your muscles, tissues and of course the bones. If you don't do the stretches right your could permanently damage something in your body. Usually when you are doing something that deals with flexibility exercises like gymnastics you should start it at a very young age because your bones are just starting to grow like for example: when you buy a plant that is baby and you don't like the way the stem is position you can bend it to a different position and the flower keeps growing thats because you are working its flexibility. This is a great example of our muscles and bones. Don't do the isotatic stretches at an adult age because it will damage the insides of your bodies.
Hope this helped :)