Cursitor Doom explained :
Back in the 1960s, when tubes were coming into service more and more, it
was a widely held belief that they were more expensive to run than
tungsten filament bulbs if turned on for short periods. It was said that
most of the power they consumed was drawn during the 'strike-up' phase so
if they weren't on for at *least* an hour, you might as well be using TF
bulbs.

That is what I was taught, but the calculation also involved wear and
tear on the tube/starter/choke. I still will not install any sort of
discharge lamp where it is liable to constant switching though.