1 You should never turn off your computer.
Your computer is designed to handle 40,000 on/off cycles. If you are an average user, that’s significantly more cycles than you will initiate in the computer’s five to seven year life. When you turn your computer off, you not only reduce energy use, you also lower heat stress and wear on the system.
2 Turning your computer off and then back on uses more energy than leaving it on.
The surge of power used by a CPU to boot up is far less than the energy your computer uses when left on for more than three minutes.
3 Screen savers save energy.
This is a common misconception. Screen savers were originally designed to help prolong the life of monochrome monitors. Those monitors are now technologically obsolete. Screen savers save energy only if they actually turn off the screen or, with laptops, turn off the backlight.
4 Network connections are lost when computers go into low-power/sleep mode.
Newer computers are designed to sleep on networks without loss of data or connection. CPUs with Wake on LAN (WOL) technology can be left in sleep mode overnight to wake up and receive data packets sent to the unit.
Read the full article on Eco-Friendly Computing.