Take two wooden blocks and glue/tape them to your computer desk, so they cant move, about 12cm apart.
Place your mouse in between the blocks and move it side to side so it contacts both blocks. Notice of how far your player infantry unit rotates its view while the blocks restrict mouse movement.
Position a player infantry unit against the wall of a building, facing parallel to the wall (ie. looking along the wall) and hug your player against the wall by pressing the move left (or move right) key.
Place your mouse in between the blocks and move it side to side so it hits both blocks. Notice your player infantry unit rotates its view wider than it did when not in contact with the wall.
Look at the blocks glued to your desk and think, "Why did I do that!?"