Entertainment Center Double Rails
If you have a complicated wiring setup in your entertainment center, you will really appreciate easily getting to the back of the units without having to awkwardly move connected equipment. Most single rails will not allow the unit to pull out with enough distance to actually be able to read which port you are about to connect into.
A easy trick is to use a piece of wood and place double rails on each side. This allows the unit to pull out twice as far as normal rails.