Dialogue

Dialogue is whatever the actors are saying in a film. Dialogue is not necessary for the opening two minutes of a film and many successful films don't have dialogue. Dialogue can give away a lot of the plot and mean that good acting skills are required to make it look professional and effective.

Dialogue is useful to explain the story and create a connection between two characters, it can also mean body language and expression becomes more important and noticeable. Dialogue, for example in comedy is essential for humour or in romcom to show the relationship between the two main characters. Dialogue can destroy an atmosphere or mood that has been created, also if acting isn't professional lines won't have the desired effect they are supposed to.

In this scene from wolf of wall street there is little to no dialogue used. It is what makes the scene so funny, unusual and hard to take your eyes off. Because there's no dialogue we have no idea what's going to happen and really can appreciate the skill of the actors.
In the horror/ action film dark knight there's a dramatic tense scene which is created by the lack of dialogue, between the Joker and several other groups of people. Anticipation is built up over what's going to happen and we see that even though the Joker is completely outnumbered he has control in this situation over these people who would normally have the control.
In my own work, without quality acting, dialogue would have less effect and I would like to avoid, I'd prefer to use narration or monologue because then the scripted is controlled and I don't have to worry about the way the two characters are together.