[dogscoff]

Good question.

The pictures/races contains graphical and AI files that define the race's behaviour in-game.

the .emp file contains race setup data that is used at the start of the game - how racial points are spent, emporer name and title etc. .emp files are crucial when setting up multiplayer games (except possibly hotseat games)

A race with an emp file can be added manually to a game during game setup. A race without one will generate its setup information from the AI_General file.