Friction is a motion-resisting force in physics which is typically undesired in automobiles, though it finds positive use in the braking system. The resistance of friction also turns energy into heat, though the heat created by air friction on the vehicle body creates much less heat than unlubricated metal sliding rapidly across metal, which is avoided in an engine through the use of lubricants.
Reducing Friction
Anything done to reduce friction within an engine can improve its efficency in all areas, and extend its working life. Motor Oil is constantly being improved to be more effective at this.
Anything done to reduce the friction of the body as it passes through the air around it will allow it to travel at high speeds with less resistance, also improving efficency in a number of areas.