You may be asked to do this by the machine, by your service department to clear a code, or for periodic maintenance. The frequency needed will be determined by the machines duty cycle. The harder you work the machine the more the DPF can burn off particulate matter during normal operation. If the duty cycle is low and the DPF is not operating at a high enough temp to burn off material, it will slowly build up and will need to be put into regeneration. This video explains how to do that.