Screensavers do not save energy. Their function these days is reduced to visuals only. Turning off the computer monitor instead of running screensavers saves lots of energy.
Better yet, turn off your monitor whenever you won’t be using your computer for more than 15 minutes (such as when you’re at a meeting, at lunch, or at home). Shutting off the monitor will NOT prevent your computer from operating to check for viruses, perform backups or receive software upgrades, some of which is now commonly run over night or on weekends. When you return to your computer, just press the monitor's power button and in a few seconds you’re right where you left off.
Laptops come with all sorts of devices that a user might not need. Each of the devices – if enabled – consume energy. A laptop user that uses the build in network adapter and a cable to connect to the Internet probably does not need Wi-fi, the build in modem, Bluetooth or infrared. The same might be valid for other devices like the DVD drive or sound card.
In offices you should check with your computer support person, however, the recommendation is that most personal computer system units should be left on (with monitors and peripherals off) at night and on weekends. This permits automated security and antivirus patch protection as well as application upgrade procedures to occur during non-business hours.