I found those definitions to be a weird line. But, I believe the overall premise is you use types for large projects that many people will be interfacing with and making small changes to. You go cowboy when it's some fun scripts.
This is not limited to type annotations. The same typically applies to comments, documentation, tests, etc. It's just one of the many code quality tools available to you (at a slight cost) , and one typically applies those tools where they have the most benefit: code that is often reused or reread.