They might not be necessary on a resume, but they make all the difference when getting hired. The good news about references is that automatically including them with a resume is no more an expectation these days than it is to include your photo.
Employers take references seriously.
You should, too. The bad news is, as most of us casually throw the above phrase at the bottom of our resumes, or we leave it off altogether, we don't give nearly as much thought to our references as we do the resume itself. But suddenly a potential employer wants to check your references. Not a problem if you've got a perfect record, but few of us ever feel completely comfortable with this. After all, there will be some sort of conversation or writing going on, about you , away from your presence.