Old tube TVs suffered from this a lot, especially the really old ones that used thermionic valves for the high voltage stages. Since everything heated up when you turned the TV on, then cooled down when you turned it off, the thermal cycling would eventually lead to failure. The more you turned it on and off, in other words, the sooner it would fail.
This effect is much less of a problem with LCD or plasma TVs, mostly because they're so much more efficient that the amount of heating/cooling is greatly reduced. And despite what you hear about "disposable society", modern devices tend to be more reliable than older ones. Unfortunately people have adjusted to that by using things more, and in harsher ways (ever see an old tube TV hung over a bath or jacuzzi?).
There's also a big difference between using the remote to put the thing into standby, and turning it off at the wall. The standby mode will still draw power, so that's less damaging than turning it off at the wall. For a short period of non-use I'd definitely use standby. Overnight I'd want to power it off at the wall, but note that many smart devices have prolonged and often power-hungry start-up routines that are a lot more involved than just "turn the screen on".
