Less fat is needed because food cooks in its own juices. This keeps the food moist and concentrates flavors. Vegetables and meat can be cooked together for a complete, nutritious meal. Cut vegetables in small, uniform slices to ensure even cooking. A slow cooker or covered roasting pan give similar results, but the cooking time is much longer, and they are better suited to larger quantities.
Oven use is minimal, a plus in summer.
Most recipes call for cooking times of less than 30 minutes in a hot oven, about 425 degrees. You can also forgo the oven altogether and toss the packets on a hot grill. Better to do this with foil than with parchment. Meals are easy to make ahead. Assemble packets in the morning and have dinner on the table in 30 minutes that night.