It's a cheap test, so if you don't end up breeding to that stallion, you can at least know for the future. I plan on testing my mare, more out of curiosity than for breeding purposes. Her dam was an overo, but she came out solid...or so she appears. :P
Drummerboy, Lethal White is a condition that happens when two horses that are carriers of Frame Overo. It causes the foal to have a improperly developed colon. The foal is born stark white and usually dies within 72 hours painfully. They are usually euthanized immediately after identification to spare it suffering.