Sailboats have two rudders steering them, not just one!
The first one is the one everyone thinks of when you they hear the word “rudder”. This is the appendage that hangs off the back of the yacht that is controlled by the wheel or tiller and is the primary method for controlling a yachts direction.
The second one is exclusive to sailboats, as powerboats do not have this second rudder, the sails. As wind hits the sails and gives the sailboat power to drive through the waves, it also influences the direction the yacht will go as it moves through the waves.
If the sails are all at the back of the yacht, the wind will hit them and push the back of the yacht downwind and the bow upwind. This is known as weather helm.
If the sails are all at the front of the yacht, the wind will hit them and push the front of the yacht downwind and the stern of the yacht upwind. This is known as lee helm.
Having the right balance of sails, front and back, is necessary to cause the yacht to be pushed evenly and to avoid this urge to rotate.
The urge caused by the wind can be felt in the helm, and can lead to crew fatigue if you are counting on the rudder to compensate for unbalanced sails. When the yacht wants to turn upwind, simply turning the helm to leeward will make the yacht sail in a straight line, but you will have conflicting events happening. The sails want it to turn upwind while the rudder is dragging through the water trying to turn the yacht back to leeward. The result is these forces will cancel out and the yacht will sail straight! But the cost of these conflicting forces will be loss of speed as the rudder and sails need to cancel out their opposing forces instead of all moving forward in harmony.
Trimming each sail to optimum performance by following the tell tales will give you maximum performance out of each sail, but not optimum performance out of the entire system. If you sacrifice pure performance and instead focus on minimizing weather and lee helm, you will actually sail faster and with less drag.
Thinking of the sails as a second rudder, almost as an air rudder, will be advantageous in your seamanship abilities. Instead of setting the sails for power, and then adjusting your course with the rudder, it would behoove you to set the sails based on the winds and point of sail you wish to be on, then fine tune your heading with the rudder. Thinking of the sails as your primary steering method, more of a macro rudder, and your rudder as a fine tuning steering method, more of a micro rudder, will let you sail most efficiently and effortlessly.