On Writing
Most of us only write when we need communication; what follows from prevalent reductionism is that writing is a means of communication; if you do not have to communicate with anyone, what to write for? But writing is quite an evolved form of communication. In almost all communication, there are things/relationships at stake that the speaker might unintendedly lose if something is wrong in their writing/speech, so we’ve “evolved” with the ability of closed-loop feedback, ensuring that whatever we are saying/writing sounds reasonable.
This naturally evolved form of feedback can be leveraged to clarify the ideas in our heads, which otherwise would be stale in the irrational background of our minds. Whenever we write, we unfold the ideas which otherwise remained curled, showing only a single perspective. Through this process, we obtain different perspectives on the reasoning joints of ideas; this brings an entirely objective-like different level of view on things.
In this unfolding process, we reflect on it piece by piece, check its reasonability, and combine these pieces to fit their coherency. One cannot reflect in a speech in the same way because the window size available for reflection in the case of speech is tiny (10-15 words), so the coherency check is very quite limited. The result of this testing phase of ideas improves the articulation faculty. Consequently, ideas will be more discrete and organized, which leads to clarity of thoughts, hence increasing the expressibility of thoughts. We often feel that words cannot express our thoughts, but most of the time, the problem is not in the language itself but more in the faculty of production of speech.
Other than this, writing something also helps in assessing the magnitude of understanding of the subject matter and dealing with emotional and mental fucked-ness in a slightly rational way (see this)
There are a lot of sound side effects on writing as well: it helps in the essentialization of ideas. Humans usually use many filling materials in any communication to lower the entry barrier of understanding and let the idea flow coherently. But once you understand the bigger picture of the concept, to really think of it, you need to lessen the amount of this filling materials as this typically leads to unnecessary drag in thoughts. Writing by virtue of reflection allows one to take out this unnecessary stuff and focus on core ideas. It also allows one to dive deep into the concept compared to being limited to the surface[sometimes for months] in the case of everyday thinking (primarily active).
Check this article by Paul Graham on writing: Putting Ideas into Words