Water heaters are an interesting thing to question as the answer will vary so much.
Do you have hard water so that every time the water is heated a layer of calcium and limestone are added to the hot parts? Think of the inside of a tea kettle if nobody cleaned it?
If you have hard water and don't use a softener, you get lots more limestone buildup in the tank and the heating is often half wasted on heating the limestone before it heats the water, so changing more often can save a fair amount of money on fuel.
Also the heater will weigh about half a ton when you want to remove it!
One way to avoid or at least reduce the wasted fuel and added weight is to drain and flush the tank more often. That's the purpose of the valve at the bottom as it tends to get the stuff that settles more than a higher opening. Stick a hose on it and run it out to some place where it won't burn and kill the grass, etc. Look at the water coming out to see how much junk and minerals are coming out and adjust the flushing to fit what you see on how often to flush it.
On electric water heater, I look at the electrode and see how much is gone to decide if it is time to change. It is there as a metal that erodes quicker to keep the damage from the tank, so the idea is to keep enough there and not let it break off to be stuck in the tank, etc.
Kind of like bait in a mouse trap? You want the bait there to keep it working! Looking ugly is not a factor!
