Are you better off knowing or not knowing? For healthy people, is there a compelling reason to know if your genes make you susceptible to a specific disease or condition? Or are there some things you’re better off not knowing? As the cost of sequencing a person’s genome plunges, these are no longer hypothetical questions. Some scientists and doctors see sequencing as another preventative diagnostic test. But others argue that the results are still imprecise. How useful is it to know you have an increased risk of cancer when it could be twice the norm or 100 times? And some fear the strains put on the health-care system by millions of otherwise healthy people who, as a result demand further test and procedures that ultimately could prove unnecessary or harmful.