I've been discussing and thinking about the theory behind editing run-and-gun footage lately, so I really enjoyed David Bordwell's post on the use of that style in The Bourne Ultimatum and the other Bourne films.
In general, the run-and-gun look says, I’m realer than what you normally see. In the DVD supplement to Supremacy, “Keeping It Real,” the producers claimed that they hired Greengrass because they wanted a “documentary feel” for Bourne’s second outing. Greengrass in turn affirms that he wanted to shoot it “like a live event.” And he justifies it, as directors have been justifying camera flourishes and fast cutting for fifty years, as yielding “energy. When you get it, you get magic.”