Storing the water at a higher temperature effectively increases the capacity of the tank. Also the stored hot water has to be above a certain level (~60 degrees) at least some of the time otherwise it won't prevent any bugs growing in it.
I was taught as a child NEVER to use a hot shower from a water tank or drink warm water from the tap after a sustained power outage until the tank has had time to come back up to it's normal temperature... Legionnaire's can straight-up kill you via pneumonia.