What is the purpose of a title sequence and opening?

A title sequence is used to do many things. A title sequence can be used to set the tone/feeling and to introduce the film's genre. In most film's, one of the first things the title sequence will show is the IDENT. This informs the audience of what production company was used to produce that particular movie. Many title sequences also inform the audience of who is starring in the film. In my opinion the main reason for a title sequence is to set the tone for the audience and give them a feel for what is happening or what is going to happen. If done well, it makes the audience feel as if they are involved and they become more attached, it allows them to be engaged from the start.