No Official Recommendation on Leaving Computer Turned on When Not in Use
There is no official recommendation from Dell. The answer to the question depends on the circumstance. The following is a discussion of some factors that you should consider when deciding whether to leave your computer on or turn it off when you are not using it.
In terms of component failure due to constant use, it makes little difference if the computer is turned off or not; the estimated mean time between failure (MTBF) for the least reliable components of your computer exceeds 3 years, and most components have an MTBF of 10 or even 15 years. By the time the computer fails from being left on all the time, it may be time to replace or upgrade the computer.
The act of turning on the computer can put considerable stress upon the computer. This was true mostly of older computers because newer computers, even when turned off, have some electricity flowing through them. The act of turning on the computer sent a surge of electricity through the computer. This is similar to a car engine. When a car engine is first turned on, there is little oil available to lubricate the engine, increasing the amount of wear and tear on the engine. By this argument, then, you should leave older computers on all the time to minimize the number of times the computer is turned on and the number of times the components are stressed. On the other hand, leaving the computer on increases the risk that the computer will be damaged by power surges. A surge protector provides considerable protection against this danger; however, the only way to ensure that a power surge will not damage your computer is to turn off the computer and unplug it.
Brownouts can also seriously damage a computer. A surge protector cannot protect against brownouts. If brownouts happen frequently in your area, you should consider investing in an uninterruptible power supply (UPS). Therefore, you should leave the computer turned off when you do not plan on using it for a fairly long time or when lightning is in the area.
Power consumption is also a consideration. A fully powered Dimension desktop computer can consume 200 Watts of electricity, and a 17-inch monitor consumes 75 Watts. In addition, both the computer and the monitor generate considerable amounts of heat while operating. Your air conditioner uses additional electricity to keep the room cool. While the various power-saving modes of your computer can reduce the total power consumption to 1-5 Watts, even this smaller amount adds up over the course of a year. Turning both your computer and monitor completely off (by using the shutdown command for the computer, and pressing the power button for the monitor) can save considerable amounts of electricity over the course of a year.
In conclusion, there are reasons both for and against turning your computer off whenever you are not using it, even if you are not going to be using the computer for 5 or 10 minutes.