When I made my first ever resume I used my full name including middle name "Blue Cat House". When my sister reviewed it, she asked me how many other people might have similar names that I would need to identify myself so distinctly. So I dropped the Cat and just went by Blue House.
If I ever sign with initials or mark a paper with initials (documents with track changes, etc), I use three initials because I don't like the two initial set (think "fu", "bs", or something along those lines).
What I really dislike is when people identify themselves as George Smith IV. Or George Smith II. Ugh. I hate it!Junior / Senior exist only to avoid confusion between a father and son who are named identically. When one dies, the other drops the title.
III and IV exist when there are multiple living generations with the same name.
I, II, III, IV, V and so on exist for royalty because past monarchs are often referenced and to avoid confusion.
Also, you don't put the numbers on a birth certificate because it can change in a lifetime (when someone dies, you don't need to keep differentiating yourself unless you or the other person is famous).
Rules rulez!