My 1Cent (mono after all), is that what I learned here is true: a TRUE Mono Cartridge is best, no need to put my mode switch in Mono Mode.
How Much Better? a little, some, more, a heck of a lot better, depends on the individual LP, but the key is to ONLY pick up the content, NOT pick up anything that might be noise or inadvertently considered content. NOT Sum Noise.
Distinction of individual instruments and/or voices can be significantly improved. Scuffs, scratches, warps, anything in the groove can be totally ignored.
To use a stereo pickup, and sum, is to add the unwanted noise in both channels, that's MUD added to the Mono Content both sides.
It is hard to free yourself of the habit of seeking imaging. Happily, McIntosh's have other options, sometimes the best is to take the input from the MONO Cartridge, and Play that thru only 1 speaker, L only or R only, whichever sounds best in your space at your listening position which can now be anywhere. I can play my L speaker only and sit on the far end of the room at mt position on the sofa with my coffee warmer, or out on the adjacent porch.
I just changed and now have 3 arms, all with removable headshells, to use any cartridge on any arm.