Clicking the Reset button in Lightroom’s Develop module resets the image to Lightroom’s default settings. If, however, you want to zero out all of Lightroom’s settings (including sharpening and noise reduction), apply the “Zeroed” preset in the Lightroom General Presets folder.
If you have applied a preset on import, and want to reset the image to its imported state, use the History panel and click the Import state.
The video below describes how to change the default Develop module settings in Lightroom (to enable Lens Correction and/or Remove Chromatic aberration for example). Because the video was recorded when Adobe announced Camera Matching profiles (in LR2!), the first six minutes of the video discusses these profiles. However, it then goes on to explain how to set your default settings in either Lightroom or Camera Raw and even though a lot has changed since then, you can still use the same method today for changing default settings for panels other than Camera Calibration – including Lens Correction.