MIT Z-Stabilizer - original with two-way switch on front - anybody know why two settings?

I have 3 of these and find them useful. The switch as I remember adds "damping" to the line. I don't know about it but  perhaps Joe Abrams can clarify. I have found the position where the rocker is pressed to the left is always better in my system. They add value in my reference Spectral/MIT system.

Thanks so much for the response ptss. I have unearthed my 3 Stabilizers which I haven't used in years since a major move and now regret so as the improvement is quite audible in my EAR/Croft/Cary electronics. So I'm sensing they rpovide a selection between 2 "different" forms of applied resonance, as opposed to "more" or "less" applied resonance.

What do you mean by 'resonance"?