They are an unintuitive, secondary way to do something that's already intuitive (i.e. intentionally selecting text and creating a comment). They are a bad/unnecessary feature because:

• You can't even see them until you hover in the right place.
• It's difficult to see which bubble corresponds to which line, because they're all the way in the margin.
• Hovering these bubbles (even accidentally, which is easy because they're invisible) will change your text selection, which is never desired. This would be helpful in identifying the corresponding text, except the selection sticks and the margin bubbles stop appearing.

It's bad UI/UX with no purpose. Remove them, please.