OK....let's use the tea urn analogy. You can produce tea one of two ways; you can fill up the urn, get it nice and hot and keep it hot. When a customer comes in you have piping hot tea available immediately. Alternatively you can dispense with the urn and wait for a customer to come in and just heat up enough water to make a cup of tea for them.
To keep it simple, lets assume that during the day you use up exactly the volume of water in the urn. You will have heated up exactly the same volume of water using either method, to the same temperature (100C) so the energy required to do that is the same. But during the day, you also have to keep the water in the urn warm as well, so that's extra energy.
So why use an urn? Cos a customer wants a fast cup of hot tea. If you boil each cup of water it is more energy efficient but slower
. But in typical Spring (and Melbourne) fashion, the maximum may drop below 20°C on Monday, then back up to 30°C by Thursday and (apparently) 16°C by Friday 
. Like a bloody yoyo... up and down like a <<<well, you can insert your preferred simile here 
>>>
. I just looked at my indoor-outdoor thermometers (I have 1 each for the kitchen and my bedroom), and instead of showing 34°C outside, they're both showing 27°C (actually I just checked again, and the kitchen one says it's 25°C outside), and the previously-northerly wind is swinging around to be a southerly. This means that because Melbourne metro area sits north of Port Philip Bay, a cool change generally follows the wind direction change.
