Electric, Plug Holder 4.5V/12V what is it for?
While researching information for this question, I stumbled upon the answer but thought I would post anyway to share my findings.

The Bricklink entry for the 9700 Technic Control Center set has a secondary picture which is the front cover of the instruction booklet.


The 5  Electric, Plug Holder 4.5V/12V elements can be seen in use as holders for the shorter wires connecting to the motors that make up the model. Using the holders provides easy access to plug in longer wires from the control center unit. The holders are necessary because, unlike the connections on later 9v wires that can be built into a model like standard pieces, the connections on the older 12v/4.5v wires cannot.