Turning standard copper pennies into silver and gold pennies is a classic science demonstration. Obviously the copper is not being converted to actual silver or gold. The copper penny is added to a basic solution of zinc and sodium hydroxide. This causes the zinc to electroplate onto the surface of the penny. Fresh metallic zinc looks like silver, hence the trick. For the gold trick, take the "silver" penny and heat it in a flame. The zinc and copper will form brass at high temperatures. Brass is an alloy, or mixture, of copper and zinc and looks similar to gold. There is no practical use for either of these altered pennies other than as take home souvenirs from a science demonstration. Actually, the only change is really of the very surface of the penny. The interior of the penny is unchanged.
If you are talking about the actual processes themselves, then yes electroplating and brass alloys are useful processes. Brass is a strong, decorative metal alloy with many uses in construction/building. Electroplating is commonly used for jewelery or decorative purposes since a small amount of an expensive metal like gold can be very thinly and evenly deposited on a cheaper base metal and yet will look no different from the outside.