Here is the late, great neurologist Oliver Sacks on the purpose of writing.
"But for the most part, I rarely look at the journals I have kept for the greater part of a lifetime. The act of writing is itself enough; it serves to clarify my thoughts and feelings. The act of writing is an integral part of my mental life; ideas emerge, are shaped, in the act of writing.
My journals are not written for others, nor do I usually look at them myself, but they are a special, indispensable form of talking to myself.
Over a lifetime, I have written millions of words, but the act of writing seems as fresh, and as much fun, as when I started it nearly seventy years ago."