A good direct can set the tone for a film in the first shots. If its supposed to be a rollercoaster thrill ride then some opening pans of a field on a foggy day would probably make the audience antsy and impatient, likewise opening your movie with the final stretch of the Boston Marathon and then make the audience endure 90 minutes of two actors talking at a restaurant table in real time and you have an audience that gets bored quickly.
Its cheap psychology, but it works.