Though friction has many disadvantages it is considered as a necessary evil. What causes it? We cannot do anything without the force of friction. If there was no friction, the motion of a body would not cease at all and continue perpetually.
Due to friction, a nail is fixed in a wall. It became possible to construct buildings and houses because of friction. Friction has made it possible to write on a paper with a pencil or a pen. We can walk as there is a friction between our shoes and the ground. We can change the direction of motion of a car owing to friction. Using a parachute it is possible to descend safely to the ground by harnessing the air resistance. In spite of having so many advantages we have to suffer a lot for friction.
Because of excess friction the vehicles cannot move easily. Any device that has moving parts can wear out and tear due to friction. In any type of vehicles- may be car, boat or airplane, extra fuel has to be spent to overcome the excess friction. Fuel energy is being wasted because of friction.
The energy that is wasted for friction mainly appears as heat energy. Not only that energy is converted to heat due to friction, but also the parts of an engine may be overheated. As a result of friction, the soles of your shoes wear and tear out. So to make the life and works easier we need friction but excess friction is the cause of many losses too. Therefore to produce the necessary friction, we have to control it. Sometimes we need to increase or decrease friction by some processes. Therefore, we cannot discard friction totally; also friction is beneficial to us in many cases. For this reason friction is called a necessary evil.