This is indeed not only relevant to Documentary but is evident is most type of film making. The film often mirrors the experience, understanding and politics of the director.
Activism could be defined as activities engaged in by individuals to change there of others situation.
Activists are generally doers - rather than watching television and thinking about the world they will put there energies into doing something 'active' to change the (political) situation.
There is also an artistic element which is lead by the film maker. Issues of what is reality and objectivity are as always relevant as someone is going to edit the film.
It simply is not cost affective to cover stories from independent sources.
An office occupation is another example as not only douse it disrupt the activities of the organization it also can raise the media profile of the campaign.
While mainstream media is led by profit, ratings and popularist culture and filtered by the current political climate, Alternative Media is lead solely by the convictions of the campaign and film maker.
Due to the political nature of film, partisan film making, especially where the subject is close to the film makers hart, tend to be the norm, rather than the exception.
Indeed it can be argued that to make a powerful film you must care about the subject, therefore powerful films tend to be both political and partisan in nature.
Inherently participatory in nature, Community Video focusing on using video to enable communities to communicate amongst themselves as well as with others.
The power and appeal of Documentary is the way it alters and plays with the way the viewer relates to and understands the subject.
The finished product is often of less importance than the skills and confidence gained through the process and the way in which the community is strengthened through people in it work and are brought together.