the idea behind the calibration feature is to set new boundaries 
within which the sensor can see the bright IR spot (from your sensor 
bar or otherwise). Remote Buddy will then use these new boundaries to 
interpolate the sensor position to the mouse cursor position on your 
screen.

Unless you have an unusual setup, you shouldn't touch that option, 
though as the default settings work just fine for regular setups.

You can go back to the default calibration data (the Reset button 
won't do that) by removing either the data for the key CalibrationData 
in the com.iospirit.remotebuddy.jp.n.vm.*.plist file in ~/Library/ 
Preferences/ - or, if you haven't invested time in reconfiguring 
buttons, by just deleting that file. In either case, removing or 
changing that file should only be done while Remote Buddy is not 
running.

Best regards, 
Felix