Homebrew PCBs

It makes a world of difference in critical analog circuitry and in 
digital circuit to reduce EMC issues. With the ground plane, you 
reduce the inductance of the traces, and if you run the numbers, you 
and create a controlled impedance trace which is critical for high 
speed or RF circuits.

Another reason is to reduce the amount of copper in the waste stream. 
I found lots of dead copper in consumer gear years ago in addition to 
ground plance, and found out it was a way of reducing cleanup costs. 
Important for the homebrewer who treats the waste himself, as well as 
the high volume consumer places trying to save microcents.
Ron