I didn't pay much attention to it at first, until I started keeping a log of all the players in Ilium (Iwaku's current mass RP). It was getting to be such a headache for people to keep track of which character belongs to who and who is doing what and who has what plots going on with who else... you get the idea. In a small RP of five, ten, even twenty something players it's not so bad, but when the RP world has 100+ characters it's no longer effective to keep track of things just with your brain because @_@
Anyway so I created a directory of character name and user name where the user names would link to actual profiles for ease of use. It was at that time I started using (and noticing) the profile numbers. xD
I'm weird like that.