While the economics may not always be clear, many farmers are looking to cover crops to keep the soil covered,
recycle and/or fix nutrients, suppress some of the weeds that may otherwise grow, and improve soil health and functioning with additional organic matter. Cost of seed, planting, termination and other management has to be weighed against expected short and long term benefits.
The choice of which cover crop(s) depends on objectives and needs, and also capabilities in terms of planting, management and termination.
Although cover crops can provide soil cover for erosion protection, weed suppression and soil improvement, each crop has their own benefits.
Check out the research from the University of Wisconsin Extension.