My first reaction is to think it’s a pity to shorten a beautiful name down to initials, BUT on the other hand we did call our Zephan “Z-Boy” for awhile (Z is such a fun letter to say!). A friend of my [name]BIL[/name] goes by “H” – I have no idea what the man’s name is other than H! My friend calls her daughter [name]Penelope[/name] “Miss P” and one of my sisters is sometimes called “T”. So I guess I don’t mind one-initial inventions but find first-middle abbreviations like T.J. and A.J. particularly dull. Which may be kind of strange, but there it is.
In general though, I prefer:
Unusual invented nns such as Edge for [name]Edmund[/name] [name]James[/name]
Interesting derivatives such as [name]Ian[/name] for [name]Caspian[/name]
Historic nns such as [name]Sadie[/name] for [name]Sarah[/name]
Naming your kid A.J. or Ayjay or A-J or Aj? Not for me. Seems like it could be awfully confusing.
Of course, you could also use just an initial for revenge like H. [name]Norman[/name] Schwarzkopf, haha.