In many cases it is recommended to plow the field before sowing.
One advantage is that it has a direct effect on the number of pests that are present in the field. A lot of pupae and larvae that are present in the soil will either be deeply buried, so that they cannot emerge anymore, or they become exposed to the heat of the sun or to predators (insect eating birds, mice, carabid beetles, etc.). This will reduce the initial number of pests that can begin to infest the new crop. Plowing will also remove most of the weeds, which would be competing with the crop for water, light and nutrients.
Another advantage of plowing is that generally the plants will develop better in well-prepared soil. The roots can develop faster and deeper in a loose soil, which will result in stronger and healthier plants. Plowing also allows rain to penetrate faster instead of running off the surface.