Air filters have a relatively standard purpose. As air carrying various particulates and debris passes through them, they trap and collect the particles to purify the air stream. However, different types of filters complete this task in different ways, depending on the kind of particles you need to filter out of the airflow. Some collect wet particles, others target dry particles and some types can even remove vapors and odors.
When you use a compressor, every cubic foot of air that passes through contains millions of foreign particles, all of which can collect and damage or inhibit your tools. These particles include water droplets, oils, dirt, dust, bacteria and, potentially, pieces of heavy metals, such as lead, mercury and cadmium.
If the air passes through unfiltered, it can cause contamination of the control valves, swell the protective seals and cause premature wear, all potentially leading to equipment failure and a need for repair.