Interesting responses. Given the lengths to which audiophiles routinely go to try to improve their systems, it's odd to hear the epithet "impractical," which suggests an unwillingness even to try it and see how it works. Of course there is no guarantee that it will work in your system, but anecdotally it has worked in a number of systems.
The idea is not to turn anything off, but rather to unplug from the preamp the interconnects running from those source components that are not currently in use. Ie, at any one time, there would be only one source component with an interconnect plugged into the preamp, though the other source components could/would be plugged into the electricity and turned on.
So, if you are playing a cd, the interconnects from your other components would be unplugged from the preamp.
In fact, my preamp has only one source input, making the issue of shorting plugs irrelevant.