Copper makes up the majority of electrical connections in kitchen appliances because of its cheapness and electrical conductivity. Pipes under the sink are typically copper as well, because it also resists corrosion.
Copper is a softer, more malleable metal that is less affected by water than iron or lead, so most newer homes use it as a material for pipes rather than lead or iron.
Cookware can be made of copper as well, and can provide more efficient cooking time because copper has a higher thermal conductivity than steel and cooks food more evenly. However, it can react with acidic foods. Copper pots with stainless steel or tin lining can solve this issue. Utensils have the same issues; it's best to use copper utensils sparingly to prevent copper from leaching into the food being prepared.
Larger appliances like refrigerators or sinks are available in copper, providing a warm color to the kitchen to make it look more inviting. Warm colors can look more natural than the stark appearance of stainless steel.
It's also possible to get accessories that have a copper finish if the homeowner only wants the appearance of copper, such as oven and refrigerator doors with a copper finish.