In conventional tillage planting, the soil is tilled with a plow and/or disk.  If soil erosion is not a major concern, tillage is a good way to eliminate some weed competition and to prepare a good seedbed.  Seed can be broadcast or drilled, however, rolling the field with a cultipacker before and after seeding will improve the seedbed quality.  Rolling prior to planting firms the soil and prevents seeds from being buried too deep.  Rolling after planting insures good seed/soil contact.  Rolling also takes the “fluff” out of the soil, which helps retain soil moisture.