I find it especially helpful to add location when posting a photo of some landmark or public event. I wouldn't tag tweets by location when I'm at home, but if I'm out it's a neat way to complement the tweet.
I have about 5 Richard Johns using my Gmail address. No matter how many times I email their contacts back asking them to update their details, I still get a few emails a day for the wrong person!
I'm currently getting spammed by match.com for one of them.