Writing is creating readable ideas. Stephen King calls it telekinesis, but I prefer to call it mind upload: you're not just currently reading my mind, I'm also going through time and space to deliver a photography of my consciousness.
This extraction process is cathartic. It helps us reflect to better navigate the trouble waters of life.
When we write, a tiny part of us becomes immortal. In fact, writing is probably the closest we have to immortality.
Reading about someone else's thoughts always feel more vivid than a thousand pictures: ideas do not age.
The more you write, the more complete the virtual consciousness becomes. This isn't science fiction, there already are machine learning libraries capable of reproducing your writing style from pre-existing content, or faking your body language from a single video.
If we take a more pragmatic approach, the biggest implication to writing is professional: if people can pick your brain or read your mind, you naturally create trust and attraction. Understanding a stranger is creating sympathy, and potentially, respect that will lead to a partnership.
Writing is evident: if you don't do it for yourself, do it for others by leaving a legacy.