I'm not that AR - ;-)

In power supplies and other DC circuits with AC mains, there IS an earth ground on the AC Mains side if using a 3-conductor supply. So, when I see that someone has used the symbol for earth ground on the DC side of the circuit, it makes me wonder which "ground" they really mean.

When you build an electronic project, you tend to separate the grounds a bit, Logic ground is a dirty type of ground, Analog ground is a reference. Then you might have a high current ground. Then at some point, you connect them together,

An Isolated ground generally means there's not Neutral/Ground connection. USB, for instance happens to use ground as a reference.

In automobiles, the sensor "ground/common" is usually brought back to the ECU and not a random Chassis point. There are also specific connections to the body of the car.

Professional audio uses XLR differential connections. They transmit the audio over a twisted pair with equal excursions above and below ground. Twisting reduces electromagnetic interference and shielding reduces RFI. It's important in a shielded cable that the shield gets connected at one end to avoid a loop.

 

USB common is also at Earth (service) Ground, in the case of a tower P.C. etc.
Max.