the car im looking at has a set of these with it, and i dont even know what they are for, they had to be taken off for compliance, does this lower the car? if not what are they meant to do?
Coilovers are a type of supension that uses a different strut. The whole strut must be swapped out and replaced by a coilover unit.
Coilovers benefit from adjustability. Most Tein units have adjustable height and other more expensive ones have adjustable dampening. Rebound, preload or camber can be found on the more expensive versions.
Well technically any damper which has a spring around it is called a coilover.
Typically though, people are referring to the 'adjustable suspension' which, depending on the model, allows you to adjust the ride height, damper rate, camber etc.
Generally, it's a pretty common item to see on imported cars and is a pretty good bonus if you can score some.