Efficiency: Multiple choice questions allow a large amount of material to be tested in a small amount of time, whereas other tests may require the taker to use up a large amount of time to write out responses. Grading is also quicker, as most tests are now graded using optical readers.
Universal: Most subject matter can easily be broken down into multiple choice selections, thereby allowing easier standardization of testing practices.
Neutrality: The taker is graded purely on his selection of one (or more) of the pre-determined responses, and the test doesn't allow the grader to introduce personal bias or misinterpretations.
Response clarity: The responses are independent of the taker's ability to express himself clearly with language or handwriting. This eliminates a source of errors and makes grading simpler.