Fiction: While leaving your computer on does lead to higher electricity bills it does not tend to decrease the functional life of a computer. Most moving components in a computer are expected to fail after five year of use, which is about your computer will start having problems running the latest software. Most non-moving components actually prefer to be in a constant state rather than being turned on or off. There are damages done during power on and due to heating and cooling the circuits, which accumulate over time. As long as you clean the fans once in a while and make sure your system does not overheat leaving it on should cause no problems.