When dealing with structures that have bad guys in them, sometimes you need to secure the outer perimeter to prevent anybody from getting away or to keep people from getting in to help them out.
A simple, manpower friendly, technique to accomplish this is to place an operator oncorners of the building. This way, with only two people, you can cover 360 degrees of an average size building. This set-up is truly more effective for observation+intelligence purposes than it is for setting a “solid” perimeter. I have been on a corner like this only to have a guy bail out of a window in the middle of the wall and take off running. At least I saw it and we were able to deal with it, which is 90% of the game in most civilian operations. Depending on the structures size and composition you also need to keep over-penetration in mind.