Hello regarding laptops

No it won't hurt anything as long as your fan works, even then a quality laptop would have an automatic shut off for over heating! I leave mine on all the time and have automatically set my spyware to run I also clean and defrag the system at night plus do the updates at night! This keeps it fast and trouble free for the morning, I'm a power user and at the end of the day it gets pretty slow! tdemex

In my case, I sometimes leave my laptop turned on for a week, I did this several times already and I my laptop is still fine up to now except that I noticed the battery life decreases from 2 hours to 1 and a half.

Nothing will happen to the laptop except overheating even if the fan is running. The performance of the system will somewhat low.That too for a short period of time only. If we switch off the system and allow the heat to dissipate, then it will work well. But if we keep the laptop in hibernation, then it seems the laptop will release some harmful gas like corbon monoxide which will affect the environment as well as the others.I happened to read about this in some discussion in mylot two days back. I am not sure as how far is it true. But there may be some possibilities for that also.