I'm really paranoid about my new monitor. Is there any difference between leaving the monitor on to idle (screen goes off, but the unit is still on), or just turning it off? Does either one promote a longer lifespan?

Answer:
It doesn't make much difference, in my opinion. In standby mode it'll probably use about 5 watts or less (depending on your monitor) compared to zero when it's off. If you're concerned about your electric bill, turn it off.

Leaving it on standby doesn't really hurt the monitor, since the display circuitry isn't really being used. For all intents and purposes, the monitor is off. The only component using up power is the circuitry monitoring a signal from the Computer, and that uses up very little power compared to when the monitor is awake.

Frequently turning a monitor on or off may injured the power switch if it's overused, depending on how robust the switch/power button is.

All in all, I wouldn't worry about it. If it's an LCD monitor, LCD Monitors are pretty sturdy even if they're on all the time. The only thing that might die eventually is the LCD's backlight, but that has a pretty long life, probably longer than most ordinary CRT's.

Either way, there's probably very tiny risk of ruining your monitor.

Answer:
There’s no difference,but it depends on your kind of monitor.

For some Monitors the power indicator goes off totally after some time.The monitor has a mechanism to cease the flow of electric current inside it after some idle time.

For some Monitors the power indicator does not go off absolutely ,it only changes color (e.g. from green to red ) and thus current is still flowing.For that kind of monitor make sure you turn it off.

When current is flowing the monitor is being used thus the lifespan will be reduced.

Answer:
it`s not different`t that you turn it off or not !

your display power will be off after some Second when signal go off form your system !

in standby time there is less usage of electrical by your display

so you can leave it in standby there’s no problem company Design adapter to work well even in standby

Answer:
the longer you leave any thing running the hotter it gets the the more likely the parts in it, if they’re soldered together to weaken or separate. Turn it off! Plus, it saves power… which saves you money :)