I have two turntables, plus four Acoustand tonearm pods. Currently using just two of the pods, so I can have four SME tonearms (IV x2, V x1, 309 x 1) on two SME turntables. Why?
Well: my best stereo cartridge is a BM LP-S, but it's only just a tiny bit better than the London Decca Reference. Then there's the BM Ruby 3 converted to mono (by Steve Leung) for mono LPs, and the Nagaoka MP-500, which is good in its own right, but also it the one I use to play disks for the first time in case there is some fault that could tear the stylus off. I'd rather replace a stylus than send an MC off for a re-tip. The tonearm pods are all on sharp spikes, and weigh 10kg each: a good cartridge mounted on an arm on one sounds better than a poor cartridge mounted on the built in arm. The VTA adjustments of the pods are far easier than the native SME adjustments, and can be changed during play, if that's your thing (not mine: set and forget is me).
I could simply play everything on the LP-S, but this way I get some variety and make the styli last longer, along with the super quiet mono playback from a true mono cartridge. I'm happy.