There are pros and cons to both ways depending on the application. If you have acres of land to farm in a certain time frame, tilling may be the only way to do it. For home gardens, though, the benefits of less weeds brought to the surface, improved soil health through less erosion, and increased organic matter in the top where the roots are means that no-till is better. And while USDA scientists say a benefit of tilling is to bury carbon and increase its storage in the soil "overall, intensive tillage tends to burn up much of the soil organic matter, more so than no-till." (source) Also tilling can do more harm than good by removing any plant matter covering the soil which leaves it bare. Bare soil, especially soil that is deficient in rich organic matter (which the tilling removed), is more likely to be eroded by wind and water, leaving it "dead soil" that needs lots of fertilizers to grow anything. (source)