Leaving a TV on all the time is okay and I do it sometimes when I'm alone in the house and want some background noise going while using the computer, cleaning house, cooking etc.
Sometimes it's nice to have some noise going to make me feel better when alone in the house so on those days I leave the TV on even when I'm not watching it.
I will occasionally go sit on the couch and watch some TV but I don't spend a lot of time watching TV or I'll sit on the couch on my laptop and be staring at my laptop and working or browsing the web while having the TV on for the noise.
The only thing that will happen if you leave your TV on all the time is it decreases the lifespan of the TV and uses more electricity.
But I usually like to buy a new TV every 5 years or so for the living room anyway because I get bored of the old TV and just want a new one.
So if I can get 5 years out of a TV I'm happy.