How does this floating shield work?

On this well regarded schematic the shield is connected by a resistor to the output. How is this better than tying the shield to the ground? Regarding its working mechanism the only guess i can make is that the output current saturates the shield and pushes out the emf. Also the shield now modulates with the signal so maybe thats a good thing too if we're after eliminating non signal related influences?

Also if my guess is correct then couldnt a similar method be duplicated with an amplifier pcb by using ground pour for the output trace which would flood a whole layer of pcb?
 

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I think its to keep the very low capacitances in the compensation network from being swamped with capacitance to ground which might lead to instability or compromise the linearizing effect of the negative feedback. I am rather guessing about this though.

The problem with a ground pour is it doesn't shield effectively.
 
I think its to keep the very low capacitances in the compensation network from being swamped with capacitance to ground which might lead to instability or compromise the linearizing effect of the negative feedback. I am rather guessing about this though.

The problem with a ground pour is it doesn't shield effectively.
Right but whats the effect of coupling it to the output? Why not to the chassis gnd instead, for example.
 
Output buffer has low output resistance ,because of feedback ,so virtually not much difference than ground. But for any input or small capacitance its not same potential as ground , so it makes sence . Interesting solution