Don't leave your thoughts on platforms you don't own
When you post a reply on a website, or a social network it is left there, maybe for a long time, or eventually it will be deleted. Having a middleware between the output and the input that store whatever you write locally is something that can seem useless on the short term, but as you accumulate more data, it can be used as a database for a full text search of your thoughts, or to train a chat bot to give answers similar to yours.
The problem with such software is the interface, ideally you want to store the text after it is properly formatted, so it should be a whole WYSIWYG editor that users interact with instead of the editor offered on the website/platform. This usually feels clunky and opaque, and considering that the short term interest of logging all your interaction is very little, an implementation that is friendlier to user adoption is hard.
There are solution for editors like emacs/vim that allow you to write inside the editor and then send the text to the destination, although in this case the interest is in improving the editing experience, not in keeping track of the output.