When you’re writing your screenplay, one question to keep in mind right from the start is:
Too often we forget that the best movie-going experience is an emotional one. We are paying to be moved to laughter, to tears, to fear, to wonderment.
Advertisers know this, of course. They want you to take action–to buy something, usually–and they know that you’ll do that only if you’re motivated and that the strongest motivation comes from feeling a strong emotion. It may be that if you don’t buy product X girls or guys will be jumping all over you slobbering with lust, or if you use product Y doing the washing-up will be an orgasmic experience.
Unfortunately most of the products don’t really deliver, but it’s important that your screenplay does.
Therefore it’s useful to consider this question on several levels:
If they leave with a strong feeling at the end they are much more likely to continue to think about and talk about your work. The strongest word of mouth comes about when people want their friends to have the same emotional experience they did.
If your character has an arc from negative to positive, you have to be sure that there’s at least a glimmer of the positive at the start so that the audience will believe the transformation.
Here you have to take into account not only the emotional tone of each scene in isolation but also in light of what went before. An emotion is stronger when next to its opposite. That’s why good thrillers and horror stories often juxtapose a funny or calm moment with a shocking one.
If you find it too inhibiting to think about this while writing the first draft, use it as a rewriting tool. Check the flow of emotions and whether you need to strengthen or vary them…and enjoy the positive emotion of writing something outstanding.