I choose to manufacture custom sleeved extensions on a small level for builds, because not only are they easy to swap between computer builds. They also can be made to curve in a tighter fashion vs full sets, that have to be constantly contained, by cable combs making a less clean finish for the computer builds.
If you have ever seen customs sleeved cables with heat shrink on the end. Near the connector you would come to the realisation that the cable looks ugly. What I aim to do with all my builds that include custom cables is to make the cables look as clean as possible. Which is why I would much rather train the cables so that no cable combs are used and cut the underside cable shorter than the top when putting then together so that when the cable bends in the case it doesn't fan out into a mess of cables. To ensure the cleanest appearence possible.
I prefer to use paracord over MDPC because the finish product is nicer. And it is more malleable having you be able to swap the kit into a new build and have an easiler time retraining the cables.