I always make it a habit to search for World War I and II draft cards for just about any relative who was of an age to have registered. Besides the details on the registrant, the name of the person “who will always know your residence” can be helpful as it may give addresses for individuals who are otherwise difficult to trace.
You may even discover someone listed when you do not expect it. My uncle had been married for near twenty years when he registered for the World War II draft. Instead of listing his wife, he picked his sister Fannie–my great-grandma.