Silk TVC - wiring question for mute position

Hello,
I have a question about the wiring of the silk TVC, when used with Bal and RCA outputs as shown here: The type is STA 522A.
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What does this switch on the bottom actually accomplish? It seems to reconfigure the grounding scheme when in mute.

1000001236.png


It seems that both in position XLR and RCA, contact 1 or 4, respectively connects to secondary 1, which mutes the circuit. Why use a switch here?
The only thing that the switch seems to accomplish is disconnect pin 1 (shield) from the XLR output when set to RCA.

Why is this shown as it is and not made simpler by only disconnecting pin 1 with a spts switch?

Thanks for any pointers.
Florian