Do you use this feature in most of the collaboration tools?

In many of the collaboration tools like drop box paper, google docs, there is this feature that lets you leave a comment next to each line you write. Is this something that you normally use? Is there anything you like or don't like about this feature?

Asking for a tool we launched recently. This tool allows you to type text, insert images, insert pdfs, embed videos, and record your screen live. All this while you collaborate with others. You can check the tool out at - https://boingiboingi.com