Proper ones work. The MLR forum banned the use of spoilers at their top speed event IIRC as people were getting up to 180+ then losing control and spinning due to no downforce at the rear.
Spoilers do what the name suggests - They 'spoil' the air flow, usually over the rear, in order to reduce lift. The traditional spoiler is a simple lip on the trailing boot edge designed to break up the flow of the fast moving air that is producing lift.
Wings work in the same way as an airplane wing, but are upside down so produce downforce rather than lift. A wing needs to be in smooth, undisturbed air flow to work properly so should be mounted as far away from the car body as possible. Aftermarket wings, being mounted a couple of inches above the boot are virtually useless in creating downforce but good at increasing drag. If you watch Skylines attempting high speed runs they are usually sans wing
What boy racers call spoilers are really wings, but most aren't even areofoil shaped and are so badly designed that they actually act more like spoilers than wings, so perhaps the name is correct Most aftermarket wings produce more downforce with their weight than by any aerodynamic effect.
spoilers and wings are made for a reason which is mainly to give you better traction i suppose you call it, which holds the car to the ground better when flying around, but most people add spoilers and wings to make there car look good. i think thats answered your question.