Spoiler (click to show/hide):
This exercise really helps to practice control and forces you to closely examine how and why you draw the way you draw. In the long run, this helps to add more variety to your characters, since you can break up your standard drawing formulas and push the differences. And if you intend to be a real professional artist or animator someday, chances are high that your job will be to follow a style set by an art director.
Here's some from me:
I don't have any specific assignment for you this time. Just pick a character, and try drawing in some different styles. For the sake of practice, try picking very different styles, preferably a few that push you out of your comfort zone. It would probably help to put the same character in the same pose with different styles, however, it can also be helpful to mimic the poses and compositions of different artists as well. You needn't necessarily make a 100% complete drawing for this practice, but try to reach a presentable level.