Installing a new electric water heater in cottage. Have noted in plumbing how-to books, that an expansion tank was situated on the cold water line before entering the water heater cold water inlet.

Is this a new requirement, and what is the benefit. Water heater will be on a well, not city water supply. It will have its own expansion tank.

Also on gas fired water heaters, should you bond the hot and cold water pipes to the natureal gas pipe as well.