i didn't know if you want to turn it completely off, you have to hold the power button for 7 seconds. i have a ps3 and i didn't know that. now i know. learned something new there.
I remember reading the ps2 instructions booklet nearly 13 years ago and it said if you are not going to use the ps2 for a long time, like weeks like you go on vacations or something. its better to turn off the switch on the back.
By reading that, i think that apply to ps3/ps4 too. it should be okay to leave it in standby for everyday use or if you haven't use it less than a week.