Yeah, corners are a big issue because thats where shotgunners will normally come at you from. The other thing you have to worry about is someone charging you using a primary and then getting close enough to shotgun. If that happens, try your best to beat them to the draw and take them down with whatever secondary you have available. This is especially crucial in something like Control (or the bomb gametype in competitive) where fighting is localized around the zones most of the time and the lanes that lead to those zones. You will rarely have large scale encounters in areas that don't lead to zones. You may have one or two people trying to pinch a zone and move through a lesser traveled avenue, but most of the time people get tunnel vision.