taw saw it. Volunteering gets things done, but not the "stated thing." Charities with effective volunteering systems seldom state that what they are trying to get done may be... (what follows is a grab bag of unstated goals, feel free to add your own):
challenge the specialized professional identity of potential volunteers and encourage them to think of themselves in another light: as citizens, neighbors, people who could under less lucky circumstances be poor/at risk of natural disaster/in need of instruction... etc.
increase happiness through face to face generosity
broaden social tolerance by providing opportunities for cross-class/culture/ethnic interaction.
encourage group loyalty (AKA "team spirit") through personal sacrifice
*challenge capitalism through illustrating the power of relationships without a price