Using the same username may allow you to manually poison your own profile to make your data less useful than a shadow profile generated through stylometry
I also also create one-off usernames in addition to my 'permanent' name. That way everybody sees the permanent name and assumes I'm too stupid/ignorant to use different names, so nobody ever suspects the other names are me. (Using different emails because I do the same thing with email addresses and - when I can afford it - phone numbers).