If you look at all of the default races and even the neutral races will see that each have a few AI files.
From what I know, if you are missing an AI file the game will use a genetic file. That is unless you are using a mod. Even then it is suppose to use default AI. I am sure someone with more AI knowledge will post about it.
Even if you make a set for private use, you can still post it in the downloads section for others to use. You never know when something you make for yourself will be enjoyed by others.
Just include a credits file if any of the images are custom made.