Absolutely a must!! I would recommend a 1"X2" "DL" drip edge. This should have been installed prior to the starter row (first row) of shingles. The "DL" actually protrudes about 1/2" beyond the decking. This eliminates the eventual drooping of the edge of the shingles. Without the dripedge, the rain will run back under the decking and behind the facia. This will cause wood rot and the paint on the facia to peel. They have to pull back the starter row in order to nail the drip edge. This should be installed on every edge of the roof, including the gable ends as well. Make the builder do it right or you will pay a pretty price later.
GOOD LUCK, Bill