Currently, any user can comment on any question or answer. But this thing leads to many useless comments and even discussion is carried out by new users which is not good for any professional website.
If a permission is created for new users to comment only on their own questions and answers or on answers of their own question, till they have earned certain limit of points. This would be great for teach new users that comments is also a privilege so they should use it with care, instead of just firing comments everywhere.
This kind of thing is also implemented in Stack Overflow to stop user from miss using of comments.