The most common need for decompression
therapy is for those whose spine has, over a long time from, developed bony protrusions called osteophytes in and around the outside of the spinal cord and the holes that the nerves come out of.
This is a natural aging process, but in some it can press on the neves and cause pain. Decompression does just that- opens up room for the nerves.
Answer assisted by Aaron Stupple, Medical Student