[FrankB]

In the early days it was not uncommon for a power supply part to fail and cause a fire.
Also critters like mice & cockroaches would get in the sets and chew wires (As well as cats, dogs, parrots, and the like).
With today's sets, they are "on" all the time to respond to the remotes. Yes, you can save electricity by unplugging them too.

Here we had sets that also had the so called "instant on" feature, whee the power feeding the set was put through a diode, cutting the filament voltage in half, so the set had a much shorter warm up time. It was not uncommon for a service call problem that "The TV won't turn off", where this diode had shorted.
One other reason to unplug sets was power line surges, especially if one lived in an area where the mains voltage greatly fluctuated, or had lightening all the time.
in 50+ years of servicing, I only saw 2 sets where they had the antennas hit by lightening. However, the entire house had a direct hit from it, so unplugging would not have protected it, as nothing can protect from a direct strike.

OTOH, I did service a lot of TV sets that had power surges hit them, in addition lots of other consumer electronics also. Where I worked the PUD was famous for dropping HT lines on the house feeds. A good thunderstorm meant bonus money on the paycheck within 2-4 days from all the extra work. It was commonplace to sell these folks a surge protector after the fact. The ones we sold had a lifetime replacement warr. on them. And the company did back them totally too. Maybe only had to send back a half a dozen total in 10 years for replacement. AND the sets were not damaged either!