It's not just something your IT person says to get you to go away.
Restarting actually works. And the reason why is simple.
When computers get bogged down, they tend to get slow. Software will act up, and programs will sometimes crash.
When you shut it all down, right from the power button of whatever device you're using (so yes, this includes smartphones), whatever process the device was getting hung up on is cleared out.
After your machine's booted back up, usually whatever was causing the momentary meltdown is gone and the device can think clearly again.
So, hitting restart's not really "magic" — but you can still pretend like it is.
This video includes a clip from Channel 4 / "The IT Crowd."