OK, about open and close stance. Now close stance, I was mentioning that you and your opponent, the stomach is facing the opposite way. On the open stance is, you could be either the right leg back or the left leg back, but your opponent's stomach is facing the same direction as you.
Knowing this, why is this important? Because number one, not every fighter is a right legged fighter. Sometimes they could be a left legged fighter. Now when you go against a left legged guy, maybe you have to switch up your techniques and vice versa. If you're left legged and you're fighting a right leg guy, again, you must be prepared to fight in an open stance.
Now what else is important about open and close stances, again, depending on which leg you like to throw out, your back kick, roundhouse kick, axe kick will affect your stance. Some people like to throw their roundhouse kick with their rear leg because the rear leg is more powerful. So they'll stay in maybe a right leg back position. Some people like to throw with their left leg and, again, they'll stay in a left leg back position. That can happen.
But at the same time, when their left legs are strong, sometimes they like to switch the stance and throw a hop step roundhouse using their left leg, which affects your open and close stance again. Some people are better at throwing back kicks with their left leg. Some people are better at throwing with their right legs. Yet, you could be a rightie but throw a better kick with your left, also.
And again, this actually affects your open and close stance. Even footwork, stepping forward and stepping back also effects your open and close stance. So you must practice with your open stance and close stance so you can be prepared for any opponent.