A complete exhaust system replaces everything downstream of the catalytic converter. Its main effect is sound: less restrictive mufflers, a more pronounced bass note, and a sharper-sounding rise in revs. As for power, the gain exists but remains modest on a stock engine, because the main restriction on a production engine is upstream - the catalytic converter and downpipe.

The second effect, less heavily marketed and more lasting: weight and durability. A stainless steel exhaust does not rust, can still be removed in ten years, and weighs less than an original aluminized steel exhaust. On a car you plan to keep, it is the part you only have to fit once.