It's been a common misunderstanding in many fields of electricity about the connection to Planet Earth.
many books are filled with things people don't understand
It's there only for safety during unusual events like thunderstorms & and power company high voltage problems also to keep the swimming pool and the Neutral at about the same potential.
Lightning tends to make and follow it's own path. Earthed protective lightning rods can collect and discharge energy from local electrical fields (into the earth) reducing the possibility of lightning up-strikes, that ionize a path for subsequent larger current down strikes, (Ionized air is more conductive.)
Swimming pools are a human safety issues and water can be pretty conductive and that energized water can interfere with human nervous system function especially if completely immersed in the water. By now most modern swimming pool installations should have GFCI/RCL current leakage protection, old pools not so much.
Planet Earth does not act as a sink or sump for bad electricity.
Kind of does, like a big capacitor with high ESR. It is where lightning goes.... For audio paths the earth is too high impedance to be significant compared to metallic wiring.
The connection to Planet Earth has no impact on day-to-day AC power quality.
Any direct earthing of safety ground (also bonded to neutral) will encounter a relatively high impedance to the dirt. Current will generally flow in the lower impedance paths proportionately. I did encounter current flow once through my yard when I had a leaking water main causing a puddle of water in my yard. I tried to power a sump pump with a borrowed (mis-wired) extension cord. Either my neighbor was trying to kill me, or someone else was trying to kill him? The equipment safety ground lead was tied to line (hot) and while it did not draw enough current through my relatively high resistance yard back to the grounding rod and fuse panel to trip the fuse, I felt a tingle in my feet from several feet away. I wasn't dumb enough to stand directly in or too close to the wet puddle with electricity involved. Wet dirt is more conductive than dry dirt.
As has been shared multiple times; earth ground is different from safety ground which is different from shield ground, which is different from mains neutral. They differ mainly in function, while they are often all bonded together at some point. Then there is signal ground (I hate that nomenclature) which IMO is better thought of as audio low or audio 0V.
JR