Reason for rounded cables is mainly looks. On the other hand though, it helps the air flow inside pc cases. Although it really does nothing for the cooling aspect, but also provides a cleaner pc case on the inside. Fact is, they are not that expensive like most would think. Best part about buying pre-made rounded cables is the quality behind them.
Nothing is done-up cheap about CrazyPC's selection.
At each end of the cables are a coupling rubber boot that helps protect the ends of the cables from being hit against anything sharp. Both are also constructed the same also. But taking a close look at the quality of construction, the cables are in fact broken down into single strips of wire before shooting through the tubing. At each end you'll find the boot that covers up for a finishing touch. As for the center of the cables, where both secondary and master are the closest together, the cables have a nice finish off as well.