Should I Be Worried?

South Korea is a very safe country and perhaps part of my sense of security comes from the gazillion police officers I see EVERYWHERE. It isn't uncommon to see police buses (like the large tour/coach buses) parked two or three deep on the street. There are always one or two in front of the Chinese Embassy and two or three by the US Embassy. But the police officers also (randomly?) line up in two columns in groups of about twenty to forty. I want to know why and where they might be going in such a formidable group!