All medical conditions have codes, mental or physical. For example, when I was hospitalized for ischemic colitis, it wasn't enough for the hospital to tell the insurance company that's what I had - they had to transmit the proper code for my condition in order for my insurance to be activated. And the DSM is where the codes for mental illnesses are set.
One of the telling differences between the fourth edition - DSM-IV - and the new edition, the DSM-5, is that the definition of "mixed episodes" is gone, replaced by the designation "with mixed features," which can apply to depressive, manic, or hypomanic episodes. In the DSM-IV, the presence of mixed episodes ruled out a diagnosis of Bipolar II.
Changes like this are why you should care about the new DSM-5.
Photo: Dave Dugdale / Flickr