Drip Irrigation increases out yield mainly for this reasons:
we can water more because of the efficiency of the system, it makes our water last longer
plants don't get wet leaves - this reduces disease such as fungus, giving us more healthy plants
water drops don't "beat" plants into the ground - we have sandy soil and aerial irrigation, like rain, causes the sand to splash up onto the leaves weighing small plants down until they are stuck to the ground - more healthy plants
as mentioned, those plants that require less water don't get irrigated with plants that need more - more healthy plants
less of some soil born pests year after year because of the lack of water in the surface where they lay eggs
fruit sitting on the surface such as squash, melons, and cucumbers don't rot since the surface isn't wet
the bees can pollinate constantly without getting sprayed by a blast of water - more bees is a good thing