Anything that aids communication is a plus.
It doesn't take up much space so no, it's not excessive if you or any of your colleagues find it useful to discuss the code.
Even if you don't do pair programming, it is useful for "over the shoulder" code reviews if you don't use tools like Code Collaborator (we don't right now).
Also if you have team members in other sites (we do), it's useful for discussing code via IM or on the phone.
How can you tell them tell them to go to line 1842 if you can't see the line?
For me it's an invaluable simple little tool. Even some of our pdf specs have numbered lines, and it's amazing how much easier it is to refer to and discuss compared to the unnumbered ones.