Mono recordings and Mono switch on Pre-Amp

Hello All
I have a question regarding the use of the Mono switch on my Audible Illusions M3A pre.Occasionly I come across an album in the mono format, (aren't these generally more sought after?) and having the provision to use the MONO button,I don't know, maybe I wasn't paying atention but there isnt a difference. Is this the desired effect? That the channel (mono)should be divided too create a Stereo effect?
I use a Denon 103 stereo cart.Am I thinking right?
Also what would be the case if I used a MONO cart?
What makes MONO recordings that much better? I understand that in the days of MONO recordings they used better recording practices that's why they are supposedly better.
Looking forward to your answers

The MONO switch mixes the two channels from your stereo cartridge so as to eliminate signal resulting from vertical modulation of the record groove. Since there is no intentional vertical groove modulation on a Mono LP, what you are eliminating is pure noise, mostly low frequency rumble.
The only reason I find some mono recordings superior to stereo is that sometimes stereo mixes are very strange. Hearing voices hard panned to one side is very annoying. Hard panning tends to keep the sound close to the speaker, not free of the speaker, a mono mix keeps everything in center, much more natural. Otherwise I generally prefer stereo mixes, I hear more information vs. mono recordings as the images are more discrete, more air and spaciousness around individual images.