It starts with what kind of risk tolerance you have about your information being looked at by U.S. customs officers. There's a personal assessment to be made. For instance, if there's privileged information on your device, then obviously you have a higher responsibility to protect that information. My point is to think about what you're exposing your information to and limit the amount of information that you bring to the U.S., because it may be acquired by customs officers.
On September 18th, 2017. See this statement in context.