Friction reduces the speed of the moving objects and it even stops the motion of the object. Friction between the objects produces heat. This results in the wastage of energy in the machines. There will be wear and tear of the machine parts due to friction.

Where friction is not useful?

Friction is sometimes unhelpful.

For example, if you don't lubricate your bike regularly with oil, the friction in the chain and axles increases. Your bike will be noisy and difficult to pedal. When there is a lot of friction between moving parts, energy is lost to the surroundings as heat.

Is frictional force harmful?

Friction between moving engine parts increases their temperature and causes the parts to wear down. Friction can be both harmful and helpful, so it may be necessary to decrease or increase friction.