Games : What does the AI teammate agressivity level do?

In Grid, you can give your teammate an agressivity level. Defend, Keep, Balance, Agressive or Attack (might be wrong, going by memory)

This level is ajustable by you and is shown below the map and above the resets, at the bottom left of the screen.

I was wondering, what does that do, and what can you use it for? (strategies that can be done with it)