Leaving a laptop turned on 24/7

can you harm a laptop by leaving it turned on 24/7
and plugged in

Mostly its a question of heat. If you have a cooling dock for your laptop then you really can leave it on 24/7. Most newer laptops will not keep charging the battery endlessly, but turn off the charge function once the battery reads full. I have two laptops and have worked with several others and never had the life of a battery shortened due to being turned on 24/7. The real problem is heat. If you can keep the laptop cool then run it as long as you want.

However, since you won't be using it 24/7, keeping it running might just be a waste of electricity. So why not power it down when you're not using it.

IF YOU LEAVE A LAPTOP IN PLUGGED IN AND CHARGING, IT WILL SHORTEN THE BATTERY AND EVENTUALLY NEED TO BE PLUGGED IN 24/7 TO MAKE IT WORK!
THERE IS NO HARM IN HAVING IT ON ALL THE TIME, ONLY HARM IN HAVING IT CHARGING ALL THE TIME, ITS THE SAME WITH CORDLESS PHONES.

Some times laptops need to rest so leaving it turned on 24/7 will make the laptop go slower (take ages for a page to load) so it's best to turn it off if your not using it. Leaving it plugged in can make the battery very hot which is not a good thing. So just turn it off some times let it rest.

Yes, you could harm your laptop by leaving it on 24/7 and pluss, that might dammage your motherboard.
I wouldn't do that if I were you. That wouldn't be smart! I own a laptop and I wouldn't dare! leave mine on for 24 hours a day. As far as leaving it plugged in, that might dammage your battery but, I'm not sure about that since I'm just guessing. When I shut down before going to bed, I always unplug my plug so that way, when I use my laptop again the next day, I'll have a full battery until it tells me to plug it in again.
I'd recomend that you unplug your plug if the battery has a full charge. Please, never! leave your laptop on for that long!

There has been a long running argument in computer circles about this. One camp believes that heat cycling that comes from shutting down your computer every evening and restarting it every day does more damage than running it all the time. I believe this to be true. In my experience computers seem to last longer when left up 24/7 than shut down every evening.

I generally leave all of my computers (servers, desktops, and laptops) on 24/7. With rising energy prices and cheaper computer hardware this will change the equation. Eventually it may be more expensive to power a computer all the time than to replace it sooner.

Back when laptops used Nickel based batteries not fully discharging the battery completely now and then greatly reduced battery life. Modern Lithium batters are largely immune from the memory effect and handle partial cycles. Lithium batteries last somewhat longer being maintained at half charge and only fully charged and discharged when necessary but trying to keep up with this is too much hassle for me. I'll just replace my laptop battery a little more often. I do keep this in mind when I charge and use my iPod though. Unless I am going to use it for hours I don't fully charge it.