Research - What is the purpose of a title sequence and film opening?

A title sequence/film opening exists for multiple reasons, listed below in bullet points:

• To give credit to the cast and crew involved in the making of the film
• To set the mood and tone of the film to follow
• To make clear the genre of the film
• To introduce the setting on a basic level to the audience
• To introduce the characters to the audience
• To begin the process of 'Suspending Disbelief' - to help the audience believe the film is real
• To engage the audience and draw them into the film before it really begins

For example, an opening sequence to a film like 'Legally Blonde' does all of these things, as you can see:

In just these 3 minutes, credit is given to actors like Reese Witherspoon, sets the happy mood of the film, makes clear the teen drama genre, introduces the character of 'Elle', helps the transition of reality into film, and engages the audience completely. This is a perfect example of the purpose of an opening film sequence.