Are Trailers Important?

Yes, for both audiences and institutions, they are incredibly important.

A trailer is a vital element of promotion and a way of reaching out to the target audience to let them know that the film is coming out. It gives them a taste for the film, allowing them to see the actors/actresses involved which could make them want to see the film more.

For institutions this means their potential target audience could be growing which ultimately means more profit if more people go to see it at the cinema. In addition to this it advertises their company through streaming sites such as YouTube, Vimeo, etc as the production (or distribution) company will generally upload the video so the target audience will then be more aware of that production or distribution company, possibly raising it's popularity for future film releases.