Coilovers as the name suggests are a damper (shock) and spring integrated into one unit, So by changing to coilovers you're effectively changing both springs and shocks at the same time. The damper in the coilover will still wear out over time, but can be re-built later on rather than changing completely. Coilovers are adjustable, so you can adjust the height ( And stiffness ) at any time. That's why they're prefered by people who do alot of track work because they can have their cars high/soft enough for everyday use and low/stiff for the track. If you have a look at the D2 Coilover thread Kcorro posted a few pics which show what they look like and you can see how they get adjusted.