The purpose of a title sequnece and film opening

The title sequence tells you about what the movie is going to be about and sets the mood and also reflect the genre of the movie by using things like sound and different images. It also introduces the production that delivered the movie.
What we usually see in a film opening:

1. Title of the film
2. Hints of the narrative
3. The starring characters
4. Effects i.e slow motion, transitions