We can improve upon the natural growth process by enhancing and controlling for certain factors. The goal is to give the plant exactly what it wants, in the exact amounts and at the exact time it wants it, and that's just easier to accomplish in hydro. By growing this way you help reach the full potential provided by your plants genetics. The results are, faster growth which of course leads to bigger yields, and generally a stronger product. For me it is also easier to read my plants and correct any problems without the soil acting as a buffer. I also can't imagine not being able to check my roots from time to time; having them burred in dirt just seems so alien to me. It can be thought of as more difficult than soil, but growing is, for the most part, just following directions; in hydro, there are more directions to be followed. Also soil is dirty, I don't want a bunch of dirt and mess in my house.
Soil is more forgiving of mistakes and generally provides a better tasting product.