Using harmonics is better when you are still using a tuner. Often times people will tune at the 12th fret harmonic instead of using the open string, as that is a more accurate spot on the guitar neck to reference. I am assuming you are talking about people tuning from the 5th fret on one string against the 7th fret on the next, which you can do on all but the G string when tuning against the B string. This works when you already have the guitar in tune and need to do a quick tune on one string or so. You still need a tuner unless you have perfect pitch or perhaps a keyboard near by where you can reference one or more strings.

Stick with the tuner and try tuning with your 12th fret harmonic next time. Good luck! :o