You have spent years curating your boards. That is *your* intellectual property, in a sense. But it lives on someone else's server.
Read the fine print. You grant them a license to use your content. But do they guarantee they will keep it forever? No.
Using Notestopin creates a local shadow copy of your most important data (your thoughts on the pins). Even if the original pin is deleted by the uploader, your note remains in your dashboard.
Your thoughts are safer on your hard drive than in the cloud.