Having clean air to breath is very crucial; if you don't have clean air to breathe then you can get very ill and may get infected with a lot of diseases. Having an air filter is very necessary, and even more if your air filter is clean you can extend the life span of your own furnace. if the air filter is dirty it becomes harder for air to pass or go through so in essence your motor has to work harder and if that happens your motor can possibly blow. What a lot of people don't know is that keeping your air filter clean save you money because then it is easier for the motor and it doesn't have to use extra power to make sure the air goes through. when it has to put more energy in because your air filter is clogged, your bill can go sky rocketing. Maintaining healthy air so that nobody in your family has asthma because you can get asthma from constantly inhaling and exhaling bad air, and last but not least keeping your air filter is an inexpensive thing to do. it does not cost much to keep it clean and another tip is that you can re-use some filters all you have to do is just wash them.