Do you mean this...
1 Reset ( No Data will be Lost )
Press and hold the Sleep/Wake button and the Home button at the same time for at least ten seconds, until the Apple logo appears. Release the Buttons.
2 ERASE / Clear All Data
Go to Settings > General > Reset > Erase all content and settings
Nothing, assuming you actually mean Reset and not Restore.
Reset... press the home and sleep/lock buttons until you see the Apple logo, ignoring the slider. Takes about 5-15 secs of button holding and you won't lose any data or settings.
Reset as in Hold down the home and Power buttons until the Apple logo shows up?
It will simply reboot. It helps clear bugs and issues that may develop over time. no content is lost.
If you mean resetting it to factory defaults, that deletes all contents and sets it back to the way it was when you took it out of the box. Fresh and clean.