So what do these advantages mean for us?
From the performance perspective:
Having a spring and dampener engineered to work together is paramount to performance. One of the limitations of a typical lowering spring is that one must match the spring fairly well with the OEM dampeners. This generally means limited spring rates as well as a progressive spring design. With coilovers, you will typically find higher spring rates which means improved handling (within reason). A non-OEM spec dampener means a lot of coilover systems use linear rate springs which gives more consistent feedback as well as more predictable handling.
Ride height adjustability at all four corners gives you the ability to optimize suspension geometry as well as achieve the proper balance of a lower roll center and vehicle pitch (aerodynamics).
Adjustable dampening can be a big performance benefit when it comes to versatility. On a smoother road, or track, you can increase compression (the rate at which the dampener compresses under pressure) and rebound (the rate at which the dampener returns to resting height after compression). In turn this reduces roll, increases pressure on all four tires, and keeps weight transfer in and out of turns under control. This type of setup is ideal on a smooth road or track as bumps and moderate imperfections in the road can quickly unsettle the car- potentially causing a loss of control. On a rougher road, or track, you can decrease your rebound and compression. While this will allow for a little more body roll (which can be countered a bit by stiffening the sway bars), when encountering bumps and imperfections in a turn the suspension will absorb them more effectively without getting unsettled.
The option of changing preload/compression length of a spring is completely performance oriented. Corner balancing is the technique of utilizing spring preload (the amount of pressure on a spring set by the length) to balance a car. Production cars are not perfectly balanced from the factory as most of you know. For handling performance it is ideal to balance the weight of the car as equally as possible. While this can be a little easier to accomplish in a full race car, most people don’t want to remove interior bits from their car and move things around too much. So how can we accomplish more balance without removing parts of the car or adding weights? Corner balancing is done by weighing the car, then placing each wheel on an independent scale. Using those weights, one can calculate how to adjust the spring rate so the pressure on each tire can be close to even on each corner. This is typically done with the driver in the car as that greatly affects weight distribution. For an example, let us say we have a 350Z that we are corner balancing. For simplicity we will just do the front right to left balance. We find the weight on the front right tire is 850 lbs (or 385.5 kg) and 905 lbs (or 410.5 kg) on the front left tire. If we want to balance that out we can increase the effective weight on the front right tire by compressing that spring. If we have a spring rate of 560 lb/in (10 kg/mm) we are adjusting to correct for the 55 lb difference (or 25 kg) we simply need to calculate the increase via percentage. 55 lbs is 9.8% off 560 lbs (or 250% of 10 kg). So we simply multiply 1 inch by 9.8% (or 1 mm by 250%) so see how much to compress the spring (you can also decompress the side with the higher weight by the same amount instead).