Teaser trailers last under a minute and are released months and in some cases years before a film is released. Teaser trailers are a unique marketing tool to used build up hype and buzz around a film to ensure its success. Despicable Me 2 launched a bunch of these trailers back in 2012. Here re a couple of examples:

A theatrical trailer is usually longer and gives away more plot detail then the teaser so audiences know what the film is about and what genre it is defined as so they can decide whether they want to see it. Considering Despicable Me 2 is a sequel, this is very important as some of the previous audience may not wish to see the film. This could be because they are older or they may not like the idea of a sequel.

And final trailers are normally the ones that give most plot detail and are highest in length used to promote the film just before it is released and are normally attached to films in theatres just before the final release date.

The minions, again took centre stage with the trailers, their iconic mascot status allowed for immediate recognition to the films debut. In alignment with the existing marketing campaign, trailers are essential to whether people will see the film or not.

(Source: http://youtube.com/watch?v=AuzyODgWRp4)
(Source: http://youtube.com/watch?v=vBXE402ki90)
(Source: http://youtube.com/watch?v=1EEHUR-7XLE)
(Source: http://youtube.com/watch?v=BnKmpgnCsa0)
(Source: http://screenrant.com/despicable-me-2-trailer)
(Source: http://www.comingsoon.net/films.php?id=92833)