A good, thorough outline makes actual writing feel effortless. All the hard work has been done! You know who’s in the scene, where it takes place, and what should happen. Maybe some of the dialogue is even set.
Making a solid outline before you begin writing creates a sense of direction. You know where you’ll be going and how close you are to reaching your destination. It’s a set of specific goal markers that allow you to stay motivated as you move forward. At any given point, you will know you are X number of scenes from a completed draft.
Additionally, there’s an additional distance that you get with the outline. It’s separate from your script, though it’s based around the same ideas. This means you can add things to the outline and develop them without the pressure of seeing them in script form. The outline will never be a perfect document, because that’s not its intent. It’s meant to lead the way.
Think about it like a cartographer going into unknown territory. The map that they create can be extremely detailed, taking a long time to produce. While that detailed map may help future travelers as they venture through this land, there comes a point where additional detail becomes more decorative than useful. The shape of the coastline is important. The exact number of trees along a path towards a valley is not.
In this analogy, you are both the cartographer and the adventurer to come. First, you populate the landscape and give it a general shape. Then, as you write, you move through that place in its full detail, looking to the map as reference if you should lose your bearings.
These analogies aren’t just chosen at random. Writing is an adventure, as grand an adventure as you make it for yourself. You may not be discovering things as they are, but you are creating a world for others to explore. And much like actual explorers, this adventure should not be undertaken with reckless, aimless abandon.