I’ve been flying a lot lately, and I’ve noticed commercial jets seem to use roll (i.e., banking the plane) to make a turn. Yet, yaw (a turn in the horizontal plane) is never used. Even when circling to hold position, yaw is never used. Why is this? Do pilots think roll is more cool, or something? - Jinx 
Planes turn by banking rather than yawing contrary to popular belief. This isn’t entirely true because the rudder can be used to compensate for cross-winds but we are talking about commercial airliners under normal conditions. The main purpose of the rudder is to keep the plane coordinated at the right attitude while the turn is being made through banking. You can turn a plane just fine without using the rudder at all but it is sloppy and less than ideal yet flight students do it all the time. That is why flight instructors say “step on the ball” until they are blue in the face. There is an instrument looks a lot like a small level and when the ball moves off center, you need to use the proper rudder to put it back in center.
In case anyone wonders where I got these weird beliefs, I read it in the book Stick And Rudder and some magazine article just a couple of days ago.
Turning a plane with just the rudder is like steering a car on ice. You can change the direction you’re pointing, but momentum will tend to keep you moving in the original direction. In fact, pilots even refer to that as skidding. (Banking the plane while travelling in a straight line is called slipping, like driving sideways across a slope and slipping downhill as you go.) Eventually, you’ll start moving where you’re pointing, but it’s not the best way to do it.
It’s Newton’s First Law in action. An object in motion remains in a constant, linear motion unless acted on by some force. The wings moving through the air give you that force. When you’re straight and level, the wings hold you up in the air. When you bank, they hold you up and give a sideways force to make the plane turn.
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The wing is a big surface. It needs to be in order to provide enough lift to hold the airplane up. So if you change the airflow over the wing you get a big push.
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The vertical stabililizer is a much smaller surface. Changing the airflow over it gives a much smaller push.
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The big wings can be used to initiate pitch or roll, but not yaw.
Combine all these factors and the most efficient way to turn a plane is to roll it to one side and use the wings to give you the big push you need to make the turn.
The rudder is still used in turns. When the aircraft is banked the tail tends to ‘fall into the turn’, so rudder is added to keep the aircraft from ‘skidding’. The lift vector is also tilted in a bank, so there is less lift holding the aircraft up. Up-elevator is added to counter this.
There are two main reasons you want to keep yaw to a minimum:
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Most airframes are not designed to stand very much of it, both from an impact pressure point of view and from a lateral acceleration point of view.
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A little bit of lateral acceleration makes most people a little uncomfortable. Normal and axial acceleration, somehow were used to it. But, I heard folks complain about as little as 1/4 g laterally. I don’t understand why.
Heh. My dad had one of those station wagons with the long vinyl bench seats. In a turn, all of us kids in the back end up sliding across the seat, all squished together against the side opposite the turn.
But in a plane? No thank you.
As others have indicated, what’s considered cool is coordinated turns, during which a passenger is neither pushed left nor right (though he is pushed down into his seat to some extent). Turns done this way are more comfortable, more efficient (i.e. they use less fuel) and safer.
Darn, I was lobbying for the cool 
factor! 
Thanks, “yaw”, for the explanations!
- Jinx