Restart. I would say Restart is the simplest way to fix most of the computer related problems. Reason is most of the problems start when you use the computer for sometimes one or more programs will crash or done something wrong will end up as serious problems or popping up scary error messages. Slow down the computer, Programs not responding or even a blue screen might be possible. Simple restart will fix these problems.
Sometimes it will remain even after you restart specially if you had to pull of the plug and shut down the computer. That is simply because such shut down of a computer will not simply clear off the memory and it will not start fresh. Even after proper shut down it will not completely wiped out for couple seconds or for couple of minutes. So it is always leave your computer off for couple of seconds or minute before starting up again. If you had to pull the power off always better to do a proper shut down and start it again. It will eliminate most of the problems out of your computer.
Is it always safe to reboot? No, even though proper restart fix most of the problems there are situation where you should not restart your computer. specially if you think your computer is infected with a virus or any kind of malware it is not safe to restart. Some viruses or Trojans will get the initial trigger and give the best chance to properly installed. Like other programs need a good restart to configure and installed properly, viruses and Trojans need it too. If you feel like your computer is infected it is always good to install a good antivirus
and update it. Then reboot it in safe mod and do a full scan. There are situations where restart is not going to work.
Restart is not only solve computer problems. Even software problems will be solve. For example in Outlook sometimes emails will be stuck in outbox. Most of the time it can be solved by just closing the Outlook properly and starting it again.
Even this is relevant to humans. Small nap or good night sleep ill refresh you. You have been struggling solve a problem for hours and did not work out, but just after a small break you or a sleep you solve it. Take a break from any problem and come back to it. Much esier to fix it.