I can answer your question quite easily.
In todays market, all electronics are what is called modular
Everything is joined together through surface to surface connections rather than soldered connections.
That means one metal is wedged against another metal to make the connection.
Some of us old timers remember the gaming consoles where the game was on a cartridge (Nintendo, Nintendo 64 etc.) the cartridge had a row of copper connectors lined up in a row across a circuit board exposed outside the cartridge, that was wedged into a series of connectors rowed together inside the gaming console.
A lot of times, the games failed to work properly unless the contacts (both copper and metal plated) were cleaned using an abrasive substance such as emery cloth.
The problem is when two metals have different chemical reactions to oxygen (air) and H2O (water) they oxidize, this oxidation causes a bridge to build up between the metals and thus they no longer make a good mechanical connection.
By removing the connector and replacing it again, disturbs that oxidation buildup and thus the connection is 100% again.
Hope this answered your question.
Edited by MrBruce1959, 16 April 2010 - 03:40 PM.