I didn't really choose my username to obfuscate my identity (John Fowler, C0817, don't have my AHA number memorized), but because it is shorter than my full name. I could put my full name in my signature but I think if you know me you know who I am on here and if you don't know me then why would my name make you take what I say more seriously?
I suppose you are talking more about the IDrinkDarkLordInMyMomsBasement type usernames than the JohnF type but ultimately I don't know 95% of the people on here and 95% don't know me and so the anonymous is fine with me.
Sometimes people can be more known by their internet handle than their real name and you can have the reverse situation where it is valuable to know their internet handle if you ever meet in person, but I digress.