In winter it soaks up the heat of the sun by day and releases it at night, moderating nighttime temperatures. In the summer it acts as a cooling mass, preventing the dome from overheating. Depending on your gardening skills and soil fertility, you can figure about two pounds per square foot per year. Thus, a 15' dome can produce 300 pounds of veggies per year. The average American consumes 200 pounds per year.
Most people supplement the dome with an outdoor garden.
Yes, the dome can freeze during extended, severe cold with little sun. However, most cold-hardy plants will continue to grow once the sun shines again. Most find on average that they spend 4 hours per week in their dome. It's not a chore, though, as the dome is such an attractive place to be. The dome is regarded as a temporary structure by most building departments, as it does not have a foundation and can be easily disassembled.