EVERY horse needs to learn how to move away from leg pressure -- not just move forward from it.
Have you ever had a horse hit your leg on a tree on the way by? Well, If he was trained to move away/over from leg pressure, you could just 'push' (put some leg pressure) on that side and he would willingly 'bend around your inside leg' and move your knee away from the tree.
Your reins ONLY control the direction your horse's head is pointing; They don't always control the direction your horse goes. Haven't you seen a rider try to turn a horse and the horse pointed his head that direction but he kept going the other way shoulder first? A horse does not have to 'follow his head. He does have to follow his shoulder. ONLY your legs can control his shoulders and body. Your legs control everything behind his neck and head. So, if you ever have problems getting your horse to go where you point his head, it is because the horse has not been trained to move away from pressure from one leg or the other.
If you are 'pushing' him with your right leg while you are pointing his nose to the left, your right leg becomes your 'outside leg'. If you are trying to move your horse over to the left because there is a tree or a hole to your right, you will just push his body over, he should bend around your right leg and move shoulder and ribs first to the left (not nose first) and your right leg becomes your 'inside leg'.