Your wheels are subjected to some very harsh elements, like brake dust [iron deposits], heat, road salts, tar and paint, and without regular cleaning and protecting, the laquer will start to deteriate, especially if your alloy wheels have been curbed or have other similar damage. All the contaminates picked up can start to work their way under the damaged laquer, resulting in the worst case scenario - a refurb or new wheels.
dooka can also remove all iron traces from your wheels.