Can constant raising and lowering temp of reliance gas water heater damage the unit and/or increase utilitys?

We have a 12 yearld water heater in our house.The landlord lives with us and pays the utility bills. He is constantly turning down the temperature to 4 when hot water is not being used.Then he turns it back up when it is needed for showers, cleaning, etc... This happens about 3-4 times daily and he thinks it saves energy. I don't think reheating a 90 gallon heater 2-3 times daily conserves much energy. Plus, I don't think he has ever flushed it out.It sounds like a rock tumbler when it heats. What sucks most is having to wait to take a shower because the water is too cold. Thing is, he is ignorant and thinks he knows best.I disagree. Who is right here?