With one exception, I agree completly with Ken, who has done an excellent job of replying to your question.
The exception are CRT's!!..... They are far more robust than they used to be, and the life expectancy is now much greater....
CRT's used to suffer from inter-electrode leakage quite a lot and could easily be damaged or blow filaments if they were switched one and off in a short period of time, such as happens with electricity interruptions,.... which in some areas is quite sever...
Electricity Companies now require that all electrical equipment be designed to withstand rapid on/off/on/off of power supplies and this has resulted in much more robust build of not just CRT's but all components in a TV..
This has led to a much longer life expectancy than before!
As long as a TV's vents are not blocked up, then its perfectly OK to leave a TV on all day.
One thing I would advise is....
DO NOT SWITCH THE TV ON AND OFF WITH THE PHYSICAL SWITCH ON THE TV!!
Over a period of time this operation tends to produce hair line fractures in the circuitry behind the switch.... which causes intermittent problems, the most common of which is the TV switching itself off, or on, or change channels, by itself.....
Its always best to use your remote to do the switching.
Kind regards John.... (Retired Field Service Engineer)