Eleminating radiation from chargers
The coupling capacitance in the isolation transformer causes common mode noise voltage from the primary side switcher not the low voltage side.  So this Common Mode DC pair extends the CM noise to the laptop.  Some have a torridal ferrite to absorb some of the CM signal but when the laptop is floating there is not much attenuation unless RF caps were used to the primary earth ground. This current is limited by the Earth ground leakage test limits often 250uA or 500uA depending on country.  So the winding coupling capacitance often radiates with line frequency modulated 50kHz or whatever switching rate. Then external unbalanced mic’s often induce some of this E field into the high CM input impedance and causes nonlinear conversion to differential mode noise.

Earthing gnd shunts and attenuates the CM high impedance Signal to low levels. 
That is simply an impedance divider.

This also works with any VGA video cable as this cable has earth ground from the 3 pin power plug. 

The only risk is a ground fault to the grid could energize the metal edges of the laptop case momentarily or an open ground elsewhere but to a machine with high ground current may pass to a user touching a good ground.

A better solution would be to have a perfectly balanced high inductive CM choke with RF caps to earth ground to both shunt voltage but at lower CM noise current levels  But this adds great expense it seems so it is not done for the few that might benefit from it.