Whether you are in a "side way stance" or not, if your opponent just moves in circle around you, you will be in "side way stance" no matter you like it of not. The angle between you and your opponent can be changed dynamically.The problem with a sideways stance is it means you cannot attack or defend with your rear arm or leg, giving you less options in a fight. It also makes it easier for someone to hook-kick you in the back to knock you off balance.