It's entirely optional to take any or all, but they can be helpful in getting a handle on your character.
The character quiz comes in three forms: short, long, and longest. The shorter they are, the more abstract (but more complete) they tend to be. Answering at least one of them earns you brownie points. Choose whichever suits your fancy. The GM's favorite is probably the middle one.
You may also find it amusing to take the personality test from the Keirsey Temperament Sorter and Keirsey Character Sorter for your character. Be sure to let your GM know what type you turn out to be.