Why do detailing products warn against letting them dry on the surface?

As a product dries, its active ingredients concentrate and can stain, etch or leave residue that is much harder to remove. Acidic and alkaline cleaners, iron removers and wheel cleaners are especially likely to mark paint, glass, metal and trim if left to dry. Work on cool surfaces, in the shade, in manageable sections, and rinse within the stated dwell time.