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If the engine(s) on one side of a multiengine airplane are set to a higher throttle setting than those on the other side, the airplane (all else being equal) will yaw towards the lower-throttle side; this is best known as a technique for controlling airplanes that have suffered a partial or complete failure of their primary flight control system(s).
Are there any airplanes that make use of throttle steering during normal operation?
Yes, The Northrop Grumman B-2 Spirit Stealth Bomber.
The leading edge of the wing has an internal structure that helps it absorb radar energy. The outermost wing segment features a "rudderon" or "deceleron", a vertically-split airbrake / rudder that simultaneously opens up and down. To act as an airbrake, both the decelerons are opened, while to act as a rudder only one is. This clever gimmick goes back to the original Northrop flying wings. There is an elevon inboard of the deceleron on the outermost segment of each wing, and then two elevons further inboard, on the next segment. Finally, there is a single control surface for pitch control on the "beavertail" at the center end of the aircraft, giving a total of nine control surfaces.
The decelerons have to be opened about five degrees before they are effective, and in normal cruising flight they are left slightly open. However, this undermines stealth, so when the bomber is in hostile airspace, it uses differential engine thrust for yaw control.
Another aircraft is the AeroVironment Helios, which was solar powered and flew with ten or fourteen electric motors. The torque of an electric motor can be controlled very rapidly and precisely, far faster than gas turbines.
To turn the aircraft in flight, yaw control is applied by applying differential power on the motors — speeding up the motors on one outer wing panel while slowing down motors on the other outer panel.
In fact, in this flying wing design, differential thrust also provides pitch control:
A major test during the initial flight series was the evaluation of differential motor power as a means of pitch control. During normal cruise the outer wing panels of Helios are arched upward and give the aircraft the shape of a shallow crescent when viewed from the front or rear. This configuration places the motors on the outer wing panels higher than the motors on the center panels. Speeding up the outer-panel motors caused the aircraft to pitch down and begin a descent. Conversely, applying additional power to the motors in the center panels caused Helios to pitch up and begin climbing.
Had the aircraft not crashed, the eventual plan was to remove the elevators, the only control surface, and fly completely by differential thrust.
