Does anyone mix to mono just to hear instruments in the center?

I haven''t but I been known to have swapped channels or remixed tracks due to hearing differences in each ear. The  BRG used to put most old Beatles vocals in the center.

Were Beatles vocals not originally center mic’d? Maybe I’ve only listened to remastered albums but I feel like Beatles vocals are always at the center of the soundstage. 

I've seen "mixing" controls where the knob starts at 6:00 and rotates clockwise. As it does, it slowly collapses the stereo soundstage until, at 12:00, it is mono. Keep rotating clockwise and it ultimately reverses channel content when it reaches 6:00 again. Pretty cool but, obviously, not "pure high end" enough for our crowd.  

A little different, maybe off subject.. BUT

Trinaural processor, is why James B did it.. he was a good musician, and the reason for the analog center speaker, idea.. That’s what he told me. Something was missing? Maybe!
He said, I’d have to train myself to listen to a WHOLE new way of sound reproduction.
The way it was meant to be (according to him).. Pretty serious Jazz keyboard guy.. Heck of an amp designer...Ampzilla....

I liked it with a couple of VMPS Planar setups.. very VERY nice..  He did a "live" playback with Brian C of VMPS..
live, recorded, and played back, all the same evening..Amazing reproduction...

Regards..

Interesting oldhvy, I'd be up for demo-ing that, although part of the enjoyment of two-channel listening, for me, is based on the characteristics of the "phantom image" and, when implemented ideally, the magic that takes place between two speakers.