IMO, if the house is unoccupied the stopcock needs to be off. There's no upside to leaving it on. It also guarantees that the new occupants will know where the stopcock is in case of a future emergency.
A leak from a blown joint in an occupied house where the supply is turned off within minutes will probably cause a few thousand pounds in damage. Leave it running for 24 hours and it'll be a hundred times that.
The latter scenario has just happened to a block of flats where one of my family lives. A joint on the main supply failed in the roof. No-one, including the freeholder, knew where the main stopcock was and it took 20 hours to find (buried in the road). The structure remains sound but everything else (floors, ceilings, walls) in every flat is having to be stripped out. It's expected to be roughly a year before anybody can move back in.