Most vehicles that turn out to be difficult or problematic when it comes to cleaning them have been polished at some time or another. Waxes cause a problem when they have been applied incorrectly, i.e. when they are used to remove stains (all you achieve here is locking the stains under a layer of wax), applied to a dirty vehicle and applied unevenly.
A special formula wax rinse is used in the rinse-off water to provide a protective coat, which enhances the shine that is already there. It repels water very quickly and keeps the vehicle cleaner for longer, making it easier to clean next time.
It might not show immediately, but after six months to a year the wax will start to cause a problem. The wax degrades as a result of environmental attack (UV, wind, rain, heat and cold), it becomes rough and discolours. Water runs very slowly over the surface, leaving the dirt, black streaks return very quickly and the vehicle becomes harder and harder to keep clean.