Is compartment syndrome really bad?

Yes: Compartment syndrome can causes ischemia, or lack of adequate blood flow to all of the contents in the affected compartment. It can cause permanent damage to nerves, muscles, skin, etc.

Acute CS: It is a very severe and serious condition that can result in nerve and muscle damage if not treated. It results from pressure on those tissues, often from fracture, crush injury or lack of blood flow to the tissue.