I normally disable screensavers or set them to black.
If your talking about a visual screensaver, realistically your just using the CPU drawing images when no one is looking and wasting electricity and keeping the chips hot.
About the only reason to use a animated screensaver over a black screensaver would be to insure that it's obvious to anyone that the computer is on.
If your screensaver is just a black screen (Not a powersave mode) then I can't see any reason why turning the screen black and then back again would cause any issue. The screens are designed to update 60+ times persecond and playback games/video.
If you actually using a powersave mode where the screen turns into standby and the backlight turns off. I don't know about any problems with turning them on and off again (unless your doing it thousands of times a day). Most embedded screens in phones and tablets turn off all the time so I doubt it's an issue.
I have yet to have a LCD screen die on me, still have a Samsung 191T which dates from around 2002 the backlight is failing but it lived in direct sunlight for several years). You would have to be abusing them quite a bit to have an effect (For example running a program that flickers between all the possible colours 60 times a second for years on end).