LCD screens - to dim or to switch off?

[Dani]

Most of us have learned through the years that CRT (cathod ray tubes) - conventional screens in cockpits - shouldn't be turned off but dimmed. For enhanced life (or other reasons?).

Now with new aircraft arriving more and more with nice flat LCD screens, what do you do when you leave the flight deck?

Serious opinion and technical facts required.

Thanks guys,
Dani