Regarding the rational for having multiple turntables:
I don’t like two tonearms on the same table, especially if one is of tangential design. I also don’t like detachable head shells. Changing cartridges on an arm without a detachable head shell is not something one wants to do every day (at least I don’t). Having more than one tonearm allows one to have multiple cartridges, the arm and cartridge matched in terms of symbiosis. Why multiple cartridges? One stereo and one mono of course, but also cartridges that play music in a different manner. One may be better with large scale music, another with small scale.
Having a table for each tonearm---the arm and table matched in the same manner as arm and cartridge---makes a lot of sense. A cartridge, arm, and table combined makes a system, just as do an amplifier and loudspeaker. Having multiple loudspeakers---each with a power amp chosen just for that speaker---also makes sense if one desires to hear music played in different ways. Or in terms of excelling at reproducing small scale music (the QUAD ESL) vs. large scale (name your favorite "big" speaker).
The cartridge and the loudspeaker----the two transducers in the hi-fi chain, one at either end.