Photography is a way of documenting what the eye sees. Its about capturing that moment in time and having it on record for the rest of time. The most prominent photographs in our history have mostly been shots of great disaster or despair. Like the iconic Vietnam Napalm photo by Nick Ut or the photos taken by Robert Capa which where the only photographic documentation of the D-Day landings in Normandy. More recent photographic documentation would be the photo of the falling man by Richard Drew on September 11 2001.
In terms of advertising, the most well known documentation in an advert would be the photos taken by Oliviero Toscani for the United Colours of Benetton. This was a very controversial campaign which concentrated on depicting the issue of race or domestic abuse rather that their clothes. It sparked worldwide debate over its content, which in the end was probably what they wanted as it made the advert notoriously well known and far more successful than if it had just contained people wearing Benetton clothes.
Another example of using photography as a basis for an advert is the Canon Powershot ad, in which they staged an event in a big city square which giant paper-machet bugs that roamed around spraying smoke and interacting with the crowd. They then gave out lots of their cameras to the crowd, who then documented the event and helped create an advert.