It is because you might create superheated water, which is not boiling while being above the boiling point. Since it can start boiling at any time, it can be a little dangerous to handle superheated water.

I am not sure about coffee, but heating water in a microwave may result in superheated water, which is above the boiling point without boiling. This can be quite dangerous, as it might start boiling at any time. In chemistry you usually put a boiling chip in the water when heating it in a test glass to avoid this.

Are you saying that if I had a kbin account instead of lemmy and mastodon, I could combine them two into the same?