From referenced Daily Beast link:
....The designation makes it illegal for any U.S. entities to do business with the group in question. It cuts off access to the U.S. financial system for the organization and anyone associating with it. And the designation also serves to stigmatize and isolate foreign organizations by encouraging other nations to take similar measures
More from link
...., Gen. Carter Ham, the chief of U.S. Africa Command, said that Boko Haram are likely sharing funds, training, and explosive materials with al-Qaeda in the Islamic Maghreb. And yet, Hillary Clintons State Department still declined to place Boko Haram on its official terrorist roster