Private tags have their uses, but "identity" is not one of them. I don't know if you can add friends on Reddit anymore. You used to be able to. I'd "friend" everybody who ever said, publicly or privately, that they'd "friended" me - which accomplishes nothing other than turning names red. At one point there were over 300 people on my "friends" list. Most of them have deleted their accounts. I probably see a "friend" twice a year. But back in the day, it sure helped knowing that I was talking to someone who actually gave a shit about me... ...and this is the functionality we get simply from green vs. gray names.
It's a private tag. It could be used in so many ways, including as an identifier of sort. Personally, I'd use it to sumarize people. For example, if I was another user tagging my profile, it might say "nerd,cars,martialarts." That right there would be enough to jog my memory on people. I'm actually waiting to see if mk will implement this idea or not. If not, I'm seriously thinking about keeping a notebook next to my computer to better keep track of people I don't interact with as often on here.Private tags have their uses, but "identity" is not one of them.