When you’re shooting dialogue, using a telephoto lens reduces perspective and the distance between characters. Combining a long lens with an over the shoulder shot can result in some very tense scenes.
In The Bourne Supremacy (2004), director Paul Greengrass favours long lenses which give the impression that the audience is spying on the characters. During an interview between Pamela Landy (Joan Allen) and Wade Abbott (Brian Cox), Greengrass uses a handheld over the shoulder shot combined with a long lens to create a sense of antagonism between these two characters.
If you’re still confused about which lenses to choose for any given scene, check out this video which takes you through the basics. You can also watch Shot | Reverse Shot which illustrates the different effects created by wide and telephoto lenses when shooting a scene.