Personally for me, it allows me to dump stuff out of my noggin good or bad. That way I can stop thinking about it and move on. A form of self reflection. I have a bad habit to hold onto thoughts and go down a rabbit hole with them in an unhealthy fashion. Basically journaling but I can store things I have learned long term.
The beauty of it is Obsidian (or really any other writing app) allows you to develop a system of writing for you. I’m not the typical writer but Obsidian allows me to write without worrying about the organization so much.