Transition + Lenth of takes.

The use of montage creates a sense that these street artists know what they're doing. It does this by creating an idea in the viewers head that isn't present in the shots themselves, the montaged shots of artists preparing their paint,

 going out in the darkness with everything prepared to clandestinely paint or stencil their artwork onto a wall, bridge or lamppost,

all while trying to evade the police,

 puts the idea in the viewers head that this isn't vandalism but art. The short transition of takes due to montage also gets across to the audience that the art they do needs to be installed quickly as the police will interfere and consider what they do as an illegal offence.

This contributes to the film as a whole in many ways. It makes you understand why Bansky prefers to keep his identity hidden,

and already prepares you as a audience to see and learn about street art, the street art movement and what it takes to make it big in the street art world. It also explain to the audience why Thierry Guetta, the main focus of this film other than Bansky, would have an interest in street art and the filming of these artists.