They can still be plugged into different ground supplies. If they have different potential, you could get a large amount of current flow. If they're plugged into sockets in the same house, this is unlikely to happen.
This is usually more of a problem with audio equipment that has analogue signals with very high sensitivity. A ground loop can convert any nearby magnetic fluctuations (like say from the electricity flowing through the mains cables in the walls) into a nasty bit of noise.
This is usually more of a problem with audio equipment that has analogue signals with very high sensitivity. A ground loop can convert any nearby magnetic fluctuations (like say from the electricity flowing through the mains cables in the walls) into a nasty bit of noise.