Audioquest has a wonderful PDF that explains there cable theories.
If you have time check it out, it's a good read.
http://www.audioquest.com/pdfs/aq_cable_theory.pdf
Here is Audioquest's explanation of Running in a cable.
Important Cable Facts Running-In: As with all audio components, audio cables require an adjustment
period. This is often mistakenly referred to as “break-in”. However, break-in is properly used to
describe a mechanical change-engines break-in, loudspeaker and phono cartridge suspensions breakin.
A cable’s performance takes time to optimize because of the way a dielectric behaves (the way the
insulating material absorbs and releases energy), changes in the presence of a charge. Cables will
continue to improve in sound or picture quality over a period of several weeks. This is the same reason
amplifiers, preamplifiers and CD players also require an adjustment period. The key difference between
“adjusting” and “breaking-in” is that things don’t “un-break-in”, however, electrical components do “unadjust”.
Several weeks of disuse will return a cable to nearly its original state.
The run-in time is essentially the same for all cables. However, the apparent need for run-in varies
wildly. As with amplifiers and other components, the better the cable, the less distortion it has, and
therefore the less there is to cover up the obnoxious distortion caused by being new. Since human perception
is more aware of the existence of a distortion than the quantity, the better the cable, the worse
in some ways it will sound when new, because the anemic forced two-dimensional effect reulting from
being new will not be ameliorated by other gentler distortions. Please be patient when first listening to
any superior product.