MDR-1 mutations, exercise induced collapse, and degenerative myelopathy are just a few of over 140 genetically derived conditions that certain companies can currently test. Just to see what it looks like, I tested one of my mixed breed dogs to see what the company would find. The test required just a small blood sample which is then sent out to the lab. The company I chose to do the testing was Royal Canin and their associated laboratory. They were able to discern that she was part labrador retriever and then the gene pool got a little muddier. They came up with the most likely scenarios but because she is a true "mutt" they admitted that the rest of her ancestry was less well defined. From a breed perspective, the information was interesting, although not conclusive. From a DNA testing standpoint, I was definitely happy to know that although she possesses one copy of the exercise induced collapse gene, she does not have the degenerative myelopathy gene. As you can see from this page copied below, the company tests for a wide range of genetic conditions. This is not a complete list of all the conditions.
So, when would this information be helpful? MDR-1 testing is important for a variety of medications. Ideally, testing any dog that is at high risk because of their breed or suspected breed would be beneficial. Some conditions like the exercise induced collapse are important to know before starting training for hunting or other athletic events. If you are planning on using your pet for breeding purposes, then I would think the information would be very valuable. Nobody wants to pass along undesirable conditions if they can help it.