If I don't write down everything I will forget what I am working on. Personal projects often get delayed by random things because they don't have a fixed schedule. After a while I forget what I am supposed to work on. What I do instead is I just write an issue with nothing more than a single sentence (often just a title with no body). If a new contributor wants to work on the project then they can use that issue as a starting point to join the project and ask for clarification how I want to it to be implemented.

I personally wanted to contribute to a few projects but it was difficult to track what is currently being worked on or what needs to be done. When an opensource developer only works 8 hours a week on a project you don't want to waste their limited time by having a dozen people ask them what needs to be done and then not doing anything (because a feature might not be relevant to you but you couldn't have known that because it wasn't written down).