If you use other than a single point ground, heavy or changing current in one load can cause a voltage on what is supposed to be ground lead of another load. If that other load is an amplifier and the voltage is phased correctly this can cause system oscillation.
One example is an intercom that worked on the breadboard but squealed once it was in the box.
The fix was to move the hi-gain amplifier ground lead to a single point zero impedance point which was the negative terminal of the power supply filter capacitor. With the in-box wiring, the current through the loudspeaker was enough to put a voltage on the amplifier's ground terminal.
Another example was a direction finder display that had the Least Significant Bit toggling.
The fix was to solder a piece of #22 bus wire on top of a section of printed circuit trace. This lower impedance reduced the voltage change on that thin trace to something small enough so it didn't toggle the last digit. Since the PC board was already laid out a real single point ground wasn't practical.
