Mine are more unpredictable than that. Last night I went for an unscheduled drink for example - got back at 8.00, set the heating just before I left the pub.
Of course, I accept it's not for everyone, and I'd concede an element of frivolousness. Even I can wait 20 minutes while the house warms. For me it's probably more expensive in gas, given my tendency now to preheat the house.
It's there in the shops, I can afford it, it is of some use and I get some enjoyment out of using it, so I've got it. Should I? Dunno.