Capping unused rca & xlr connectors???

It is customary to short any unused RCA inputs on preamps. This prevents pops and clicks when switching your source selector between actual sources that are plugged in. Also prevents unused inputs picking up stray RFI. You can use pre-made shorting plugs or make them yourself. I don't recommend the Cardas caps because they don't actually short the input, but only shield the hot signal socket from RFI.

Unused XLR inputs do not require this treatment since they are balanced and self-cancel any noise.

They also keep dust and insects out.

Neil:
You said that you don't recommend the Cardas Caps....what
pieces do you like for this purpose?

If you cut the wire off all the cheap ic's you get with dvd players, and vcr's. Then just seal the end cut with a cigarette lighter, this will even allow you can keep out the insects? I'm sure everyone has a closet full of original manufactuer enclosed interconnects that are just taking up space?

Jeff, the Cardas cap doesn't actually short the input. It only shields it. So it's only doing half of what a true shorting plug does. I'm not sure who's making shorting RCAs these days. I always made my own by taking an RCA plug and soldering a wire (inside the barrel) between the pin and the ring, and then screwing the cover back on.