Your point about recording from one side of a stereo bus (which will happen if you record a mono source thru an assigned stereo buss) is hopefully informative for those that did not know about this. So thank you 
But I am also glad you brought it up because I missed specifying something in my original post. This topic was supposed to be about recording from a mono source (like a guitar) through a properly assigned mono VST Connection input buss to a Cubase stereo audio track versus recording to a Cubase mono audio track.
Unfortunately I missed adding the “through a properly assigned mono VST Connection input bus”. So I apologize if I confused anyone.
Try this short experiment for yourself to see and hear what I mean (I just did):
1 - Start a project with (1) Stereo audio track and (1) Mono audio track both set to 0dB in the mixer. Make a quick recording of a guitar to both of those tracks at the same time. Your guitar needs to be connected to your audio interface through a standard mono 1/4 jack connection and that input used must be assign as a mono input buss in the Cubase VST Connections menu.
Notice you will now have (2) tracks with a mono recording on each. If you check in explorer they show to be the same size files. When I play them back together and separately, for me, in the mixer they look and sound the same. Hopefully they do for you too.
2 - Next, assign the same VST guitar insert to each track. Choose a nice clear amp effect and add the same to both tracks. Amp settings must be the same.
3 - Next, add some kind of stereo guitar pedal (like a flanger) and add the same to both tracks. Adjust the flanger depth setting to max. Flanger settings must be the same.
Now, take a listen to each track together then separately. When played together I can plainly see in the mixer that the stereo effect on the mono track is playing back differently than the stereo track. When I listen to each track separately I can easily hear that the mono track is missing some of the stereo effect that I can hear in the stereo track.
This, my friends, is why I always record my mono sources (on a mono input bus) to a stereo audio track.
If you look on page 439 of the Cubase operation manual you will see this short note…
NOTE If you apply an effect to mono audio material, only the left side of the effect’s stereo output is applied.
The paragraph this is listed in is not “exactly” the same topic being discussed here. But… it makes me wonder.
Of course this same issue will happen for whatever audio you record on a mono track.
So why do it? Ever?
Regards 