I also come from an open wheel background. I crewed for my dad's Reynard 1986 Reynard SF200 and raced a FV. Tons of money is spent on shocks in open wheel cars and I would assume in IT cars as well. The more money they cost, the more adjust-ability they have. My dad's FC had Penske doulbe adjustable shocks on them. Because they're adjustable (as opposed to just re-valved) the user (Crew/Driver) can fine tune the setup more to the drivers liking, track, or track condition.
The main adjustable factors are bump and rebound. The more you tighten your adjustable knob for Bump (I believe it's on the top of the shock) the stiffer Bump will get. Meaning that when you hit a bump like a curb or something of that nature, the affected wheel will be more resistant to upward movement. If the Bump was loose, then the wheel would have more travel. The tighter the bump, the harder the ride. The more loose the bump is, the softer ride. Kind of like Porsche vs. Cadillac.
The second popular adjustable option is rebound. This is when the weight of the car is coming down on the shock (returning from a bump action, the front end when braking, the back end when you let off the brakes, the left side of the car when turning right, ect.) The stiffer (knob turned to right) this is, the shock will be more resistant to the cars weight(flatter around turns.)If it is softer (knob turned to left), the car will lean more around turns and during braking. This is useful especially in the rain, as making your shocks softer will allow more of the weight to transfer to your tires, thus giving you more grip.
I hope this helps, if you need anything else, or if I'm wrong, let me know.
Steven