Should water heating stay on all the time?

[Naz2009]

I've just moved into our new home and it has the old water tank system with air flow for heating. No central heater.
To have warm water there is a switch which says "warm water" should I keep this on all th time. Will this cost a lot as boiler is on all the time. I'm very confused by it all. Also is there setting to to turn water temp down?
I need help understanding this system.

Watts is the unit of electrical power
1 watt = 1 Joule per second
So once you know how much time it takes to heat up your water tank then you can convert it into the electrical power required to do the job (into the KWatts you mentioned initially).

We have this exact system and run the boiler for about 90min in the morning

The water stays hot all day (but you need to buy and insulated jackets for that tank- they're just wrap round and tie on)

It might be cheaper to run the water heat wing at a time you have the air heating running too- not sure about that one

@MotherOfCrocodiles thank you. I'll look online and buy the insulated jacket for my tanks. Appreciate your advice.