In many opening sequences there are multiple special effects used, these can be seen mainly in a lot of action, thriller and fantasy films. The main special effect is computer generated imagery (CGI), a large example of this type of special effect is the 'Transformers' trilogy, which uses CGI throughout the whole movie as they are the main characters next to Sam Witwicky. Using these in the opening sequence shows the audience the quality that will be in the film if a good CGI is used.
Also, the use of blue-screen's and green-screen's also is a massively used special effect, using this it shows the audience that they have a larger budget than independent film companies because they will have better green/blue-screen quality. This allows the audience to think that the film will have a good special effects scene. These types of special effects help gain a pre-sold audience for action genre films because it makes the film look more realistic.
Also 3D computer graphics and film may be used, which show that the film has a very large budget and that it will have a strong special effects group, this will only appear in opening sequences if the whole film is going to be in 3D.