Hi Meri, the need for an auto drain is somewhere between necessary and a good idea. There is no down side. Your steam generator produces distilled water in the form of steam. Consequently, the mineral and lime deposits present in the water remain in the tank and will eventually degrade the function of the unit. All Mr. Steam generators come with a manual drain valve so you can flush the unit at will to remove these deposits.
My opinion is that if your generator is located in a remote or hard to reach area or you are simply interested in a maintenance-free steam system, the AutoFlush, available on all Mr. Steam units, is a must-have item which will insure many years of trouble free operation.
Read more about the Mr. Steam AutoFlush