It's generally used for boards that are bent/flexed iirc.
I doubt there's much concern of noise in the frequencies we live in though. There are some quidelines/concerns for routing over it re inductance...
My understanding is it was developed to mitigate the effect of temperature expansion of different materials (copper and baseboard). It is a thing of the past I guess. You will probably not be designing a guitar effect pedal that would benefit from it.
I have used this approach also for visual effects. If you put route keepout (shape of your preference) on your board you will get this mask dip effect. I made markers around the knob with it using a PCB front panel. It was not very pronounced but a nice textural thing nevertheless.
VFE has a webbed ground pour, and Peter seems meticulously obsessive about stuff like that— doubt he’d do that if it had a negative impact considering he goes overboard on the engineering of everything else