From the DOS web page.
"Not sure what an Embassy really is? Well, it’s not just another building full of bureaucrats. In many ways, the U.S. Embassy is your 911 when overseas. Whether you’ve lost your passport, need to evacuate the country, or someone back in the U.S. needs to get in touch with you, the U.S. Embassy is your point of contact for assistance in many different situations. During a natural disaster, political upheaval, or other emergency, consular officers assist American citizens with transportation, evacuation,
and in keeping them safe. This is just one of the many reasons that we encourage you to register your trip before you depart."
http://travel.state.gov/content/stud...heir-role.html