There's all sorts of people / aliens to meet throughout the universe, some of which you can recruit, whereas others might have some sort of side objective for you to complete. (psnstores.com)
You'll get 1 - 3 stars based on your performance in the race, but two bonus stars are awarded for completing side objectives, like drifting or picking up cash icons. (slidetoplay.com)
The best example is during missions where players can take on multiple tasks such as side objectives by eliminating bonus targets as well as beating certain goals within time limits. (blastawaythegamereview.com)