Advantages
No guessing
have to generate answers rather than select them
students can demonstrate their knowledge within broad limits
Allows divergent thinkers to demonstrate originality, creativity
in contrast to multiple-choice which are terrible for divergent thinkers who always chose the answer that isn't in the list of alternatives provided
of course, leaves open danger of diverging a bit too far...
divergent thinking can be problem for marking in same way as for short answer
Example: famous court case of physics student and barometer.
Reduced lead time required to produce
less stuff to type, run-off if caught short
write 'em on the blackboard if you have to
Less work to administer for smaller number of students
easier to mark ten essays than to build a multiple-choice test for ten students; advantage decreases with class size
but also have to consider long-term: teaching this course again next year?
Can be rich in diagnostic information
one topic in real depth