I frequently make my own cables in my server room in order to minimize overrun.

The cable lengths that Monoprice offers — who offer a greater variety than most — are, in feet, 0.5, 1, 2, 3, 5, 7, 10, 14, 20, 25, 30, 50, 75, and 100. If I want to run a cable that's seven feet or less, that probably makes enough sense. If I want to run one between seven and thirty feet, it might make sense. If I want to run one over thirty feet, I'd have an average of more than ten feet of slop. If that's a couple of cables, it's no big deal, but if it's dozens, it becomes a big deal really quickly.