As TC has just indicated, "custom valving" is the more correct term. Regardless if the shock is non-adjustable, or single or double adjustable, for the most serious effort in racing/competition, having them matched to your suspension and car is another advantage to add to your vehicle. So, when you're racing in the .001 of a second, on an autocross or road course competative event, everything matters. If your competitor who just beat you had his shocks re-valved to better suite his car, and you did not, you might consider doing so.