Why clean concrete?
Concrete is beautiful when it is freshly poured. Then day after day, dirt and grime settle in. This process happens slowly until one day you look at the once beautiful concrete to realize it's an eye sore.
There is also a safety concern of certain dirty concrete. Algae that has grown the shaded part of a concrete driveway will be slick. This could lead to somebody slipping, or a vehicle losing traction.
Any sort of build up on concrete will affect how much friction the concrete has. Airports are very aware of how much friction their landing strips have. Landing strips build up rubber deposits over time. At some point, the amount of rubber on the strip will affect how long it takes a plane to slow down when landing. By keeping their strips clean, they are keeping people safe.
Cleaning concrete is not always straight forward. Depending on what type of concrete you have will determine what method should be used to clean it. Certain stains, grease spots, or surface type are factors to consider when choosin the proper cleaning method.