the best demonstration i can point to is by considering your standard three way PA cabinet.
no company in the world would ever consider loading a full range cab with just one type/dimension of speaker--
for example, a PA cab loaded with 3 - 2" compression drivers only capable of efficiently reproducing frequencies above 3k, or 3 - 10 or 12" midrange drivers, etc would sound very lame
unless they were accompanied by complimentary cabs that were dedicated to handling the neighboring frequencies, and properly crossed over and time aligned
if you've ever taken a 2 or 3 way PA speaker apart and listened to the individual drivers isolated, you would be totally unmipressed, particularly when removed from their specific cab position, yet combined and crossed over, focused properly in the right cab, you get stunning results.
i re-evaluated what gtr cabs should do when i heard r. bogner demo the uberkab at the amp shootout. that cab sounded so much bigger and dynamic than the traditional 4 v30 model, i instantly recognized the potential and soon aquired an uberkab for myself.
i tend to imagine full range gtr tone as a column, like a building, with highs on top and bass on bottom, and the different speakers you select are like placing different sized windows at different heights on the building, to reveal different elements of the bldg.
celestion uses the best "glass", use standard window sizes, and tend to put their windows in the perfect spots. EVs use thicker glass and put their windows in one spot. JBL uses no glass. jensen is the tower window with the pretty princess in it. eminence uses weird shaped windows, puts them in weird places, crooked, with heavy curtains
i even went a step further and now run 4 different celestions in my 4x12
v30, G75T, gh30, and greenback
one could point to some negative ramifications regarding differences in speaker efficiency manifesting in one speaker's volume dominating another in such a config, but i really don't hear any offensive problems.
perhaps a bigger potential problem would be slight differences in speaker dimensions, creating phase cancelations, without the use of dsps to time align the drivers as you would expect in a larger loudspeaker system, but again, if it's happening in my 4x12, i'm not being "bothered" by it.
the extreme practice of this philosophy can be found in the rivera los lobottomy sub cab and the ISP vector sub cab, but i'd argue that guitar rigs SHOULDN'T meddle in those sub frequencies most of the time, unless maybe you are going after huge arena band sounds from a trio or really modern industrial anger rock
but to me, that's what a BASS and keyboards are for, and adding the guitar sub would just create bass coupling/stage rumble that makes for muddier stage sound and FOH engineer anxiety.