Prometheus: World Premiere, London

'The cast and crew of Prometheus walked the "Blue" carpet at the Prometheus World Premiere in London.Ridley Scott, director of 'Alien' and 'Blade Runner,' returns to the genre he helped define. With PROMETHEUS, he creates a groundbreaking mythology, in which a team of explorers discover a clue to the origins of mankind on Earth, leading them on a thrilling journey to the darkest corners of the universe. There, they must fight a terrifying battle to save the future of the human race.
Genre: Science Fiction
Director: Ridley Scott
Cast: Charlize Theron, Michael Fassbender, Noomi Rapace
Release Date: June 8, 2012'

Taken from the Youtube description. A premiere helps to promote a film, as it joins the major fans of the films to one place where they can meet the actors/actresses and possibly ask them questions. This also generates alot of television coverage, as if the film has famous actors in, then entertainment channels will record the red carpet (or in this case, blue carpet) event.