This is a simple yet useful thing. If you copy paste from anywhere into OneNote it takes a little longer than usual, especially if it is from a browser page. It also shows progress bars like Contacting the server. In addition, OneNote automatically pastes the URL of the web page at the bottom of the content pasted.
In most cases this is a good thing. But in some cases, you KNOW that you just want the plain text. In such cases, you have to click Home tab – Paste Special and choose Keep Text Only. If you need this option often, you cannot add it to QAT. Adding the entire dropdown to the QAT defeats the purpose. It still remains a two click operation. But of course, there is a solution.