Clearer sound after reconnecting cables?

Well, sure.

Tiny amounts of crud and corrosion on the connector surfaces change the resistance and capacitance characteristics of the connection. I'm told that in extreme cases this stuff can even act as a diode.

For years, experienced listeners have been recommending that you unplug and plug back your cables every so often, just to clean them off.

The recommended way of cleaning them? There are more than one, which is typical of course.

The simple way is just to unplug them and then plug them back in. That will wipe some stuff off, probably enough to make a good contact again. Do it once a year when you clean out the rat's nest behind your system.

Another way to do it is more expensive. Use a contact cleaner and wipe the metal surfaces. Some cleaners also protect the surface from crud buildup. One of the most popular is Caig DeoxIT Gold.