Well, Bufus is not telling you the whole story.
What he did say is essentially correct though!
The fact is that the resitance of the cable is in the milliohms, and that a double (100%) increase in resistance is really rather small. So, it's not the resistance that you have to worry about too much.
IF there is anything to worry about it is the reactance and the effect that it will have on how your amp sees the load. In some cases (highly capacitive speaker cables come to mind) I'd actually want some series inductance with certain loads.
But, for optimizing a system, I'd have to say keep both sides the same as much as is practical.
And, coiling *one side* of a speaker cable is likely to not be as good as not coiling one side...
In case you are unsure about what the effect of "out of band" reactance is on a typical amp, try measuring a square wave with a capacitive load on it! It usually doesn't look very pretty - and doesn't usually sound so pretty either.
_-_-bear