There are a variety of reasons people till, and a variety of things that it helps, as well as hurts. Its a quite contentious issue. So far as weeds go - if yo

There are a variety of reasons people till, and a variety of things that it helps, as well as hurts. Its a quite contentious issue. So far as weeds go - if you think of tillage, it will incorporate all vegetative matter back into the soil and you end up with a clean dirt surface to plant in. Tillage in particular is useful for two reasons here - tilling is a method of quickly incorporating amendments into the root zone of plants - those amendments may be a green manure cover crop, animal manure, lime, etc. Tilling also increases new surface area of soil to air, resulting in a massive kill of soil bacteria. This "bloom" of bacteria increases nitrogen availability. This also churns up all of the weed seeds that were buried in the soil, and you will quickly get weeds in a tilled surface as they now have ideal growing conditions, where before they were buried in the dirt too deeply. So you still get weeds with tillage. The reason Roundup resistant crops were developed, is to allow the farmer to spray glycophosphate broadly, and kill off these weeds without killing the desired crop.