MongoDB MapReduce - Emit one key/one value doesnt call reduce

Question

So i\'m new with mongodb and mapreduce in general and came across this "quirk" (or atleast in my mind a quirk)

Say I have objects in my collection like so:

Answer 1

"MongoDB will not call the reduce function for a key that has only a single value. The values argument is an array whose elements are the value objects that are “mapped” to the key."

http://docs.mongodb.org/manual/reference/command/mapReduce/#mapreduce-reduce-cmd