You really should only have your coils cleaned if they are very dirty causing your system to become inefficient, or there is a dangerous mold growth on them. Coils should be cleaned if they are causing freon pressures to be low to the point of causing them to freeze up. Sometimes coils can be cleaned without removing them from the air handler, using a wire brush or hard bristle brush. In some cases where the coil can't be cleaned adequately witha brush, it will have to be removed from the air handler and cleaned with a coil cleaning solution. If you have a package unit, most of the time they can be cleaned in place with a cleaning solution. A simple brush cleaning will not remove all the debris deep in the coil. The coil cleaning solution will boil the trash out where it can be washed away. Frequent cleaning can cause damage to the aluminium fins on the coil. The bent fins can cause your system to become inefficient by blocking airflow.