The delay finder’s role is to determine the total delay of the signal path, from source to response. Note that this excludes any delays induced by your soundcard and DAW, as these should be compensated for and equivalent to zero as explained before. Here we are only concerned with the time taken by sound-pressure waves to travel the distance from loudspeakers to the measurement microphone placed at the listener position.
This figure must be determined with sample accuracy in order to establish proper transfer function and impulse response measurements. In a sound installation context, computing precise time-delay is crucial to align multiple speakers and transducers properly, as to minimize comb-filtering artifacts.