In manual transmission cars, some drivers partially press down on the clutch pedal to make the engine operate more smoothly. Some drivers even have the habit of resting their foot on the clutch pedal.
source/image(PrtSc): Learn Engineering
This is known as ‘riding’ the clutch. However, do you know that this habit is really bad for your car? This video illustrates the physics behind ‘riding the clutch’ and its consequences in a logical manner.
Never depress a clutch pedal partially. The clutch is two discs, one attached to the motor and one attached to the transmission (and through that, the wheels). The clutch pedal controls the distance / pressure between the two discs./Tim Trampedach
Press the clutch in, you loosen the pressure and increase the distance, thus letting less power go from the engine to the wheels. The power is lost through friction on the two plates. “Frying the clutch” happens when you let the two discs slip too much against each other and it the plates start to burn.