The downside is one of redundancies and time/work management; as programmers you’ll no doubt understand why having a code or language preset is always preferable to going over all your work afterwards and checking and correcting errors.
It is a lot of work to have to do at the end of a project as opposed to setting up at the beginning and having it be automated,
Creating presets is something that would apply to all a user’s books and documents. A personal annotation system can be simple or complex depending on the user. In my case, that means quite a few color scheme/hashtag combinations to remember. Could I go over all my documents and make sure they’re working according to my annotation key? Yes, but that would take a long time. I’d like to save myself the trouble. It would also help in visually recognizing annotations that go together across different documents.
Honestly speaking, I can see it saving a user hours of work on the back end.