Hello Thomas,
Currently the setting only affects the relative stereo channel (panning) amplitudes, and only if mono samples (i.e. mono WAV files) are used and played back in stereo.
Hauptwerk doesn't currently have native functionality to add reverb/wetness to samples (except by the user adding external reverb, e.g. via a hardware reverb unit or via a VST plug-in), although we do hope to add native convolution reverb functionality in the future (as well as more native surround-sound ability). The setting might possibly affect those things in the future, but for now it just affects panning mono into stereo (and only if the WAV files are mono).