as an aid in setting sensitivity and width parameters it would be nice to know the logical thinking and the mathmatical equations be used for this effect. 
Hopefully the Click Removal effect will be replaced in the near future because in many cases it is not effective.
The basic algorithm is that it looks at the peak amplitude over a short period of time (represented by the “width” parameter) and compares that to the average level measured over a longer period. If the short period amplitude is greater than the average amplitude + the “sensitivity” amount, then the short period is marked as a click.
I’m currently working on a new algorithm that will hopefully be more effective and easier to use. It may not be ready in time for Audacity 2.0.6 but if not I have high hopes for it in 2.0.7.