There are some circumstances where a person should list volunteer work on his resume. One scenario is a person who has recently graduated college. A person who is looking to change careers or returning to the workforce after a significant period of time may also want to list volunteer work.
Someone who is between jobs also may want to list volunteer work, as it accounts for what he was doing during a period of unemployment. Volunteer work that is relevant to the career field a person is applying in can be beneficial, especially for individuals who do not have a history of working in the field.