In a really perfect world, every ground should go back to the single point ground.

The first part is to have Telco, electrical and cable tie together at only one place.

The telco protector is a potential source of problems, but it's on the telco side of the NID and connected to the ground rod. Hum usually shows up in the land line.

Another issue is the cable. I should also be home run if from many locations. A splitter here and a splitter there isn't very good because of potential loops.

Each 120 V branch circuit is already a loop, because it has multiple outlet grounds in parallel separated by some distance. If each outlet went all the way back to the panel, the potential loop would not be there.

Some device along a circuit can potentially put noise on ground from say a switching power supply filter that's grounded. A fault can raise the potential of some device say near the middle of the loop from a lightning strike or ground at the end of the loop.

Ground is supposed to be low impedance and in theory nothing should happen.

Everything works really well when you have one phone, one device connected to the TV or the devices are clustered and you have a single point ground.

USB also uses ground as a common to the power supply. Switching power suppllied that are grounded also put some amount of noise on the ground. The RCA phono jack is the consumer (single-ended) version of what's done commercially using differential signals and DIN connectors. there is a in phase and out of phase signal relative to ground. The wires are twisted to reduce EMI and shielded to reduce RFI.

Shields should actually only be connected at one end, but sometimes that isn't possible.