It's all down to personal preference, if you need constant hot water and don't have a combi - then yes leaving it on all the time is beneficial, for the elderly that are in all day or during school holidays. For a working family, where the house is empty all day then it seems pointless having the boiler on.
As for the price issue i've never seen any calculations to say that leaving the hot water on all day or boosting every night costs more or less.
I think it will cost more, if you have the hot water on in an evening if your cylinder/tank is insulated the water should still be hot enough for a wash, shave, dishes etc the next morinng, keeping to water hot will cost more as the boiler will be cycling on/off all night. Many people keeping the boiler on 24/7 is cheaper - I don't think so, but again no calculations to prove it.
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