A cable question, sort of...

This is gonna sound contradictory to those who don't think about what's going on but what is true of power cords and high voltage/high current speaker cable is quite a bit different than the comparatively low voltage low current going to a sub. In this case being high level doesn't matter because the resistive input on the sub (typically 20k to 50k Ohms) means its not high level after all. As far as the wire and the amp are concerned it is a negligible line level load. Also being a sub means the high frequency range where coiling wire would be most problematic is moot. So still not a good idea but way more theoretical than anything and in the big scheme of things no it is not a problem. And if your question was will it harm the amp or sub then no definitely not.

When you "coil" up the wire, you affectively create a parasitic inductor.  If the cable is long enough that may end up to have too much inductance from the coiling affect, the parasitic inductance may create some resonance which in turn could make the bass of the subwoofer sound a bit mushy.  The question is if your cable is long enough that it will create enough inductance that it will make a difference in listening.