Cleaning of plant leaves is usually only done on houseplants, because they're inclined to accumulate a lot of dust over time. Outdoors, exposed to the elements, plants get 'cleaned' by moving air (wind, or a breeze) and rain, so its not usually necessary, unless something has been spilled over them, like maybe dust and dirt from nearby construction/building work, which may make a thick layer over the foliage of plants in the vicinity - this is best brushed or shaken off. A thick layer of dust or dirt, if left, will likely interfere with photosynthesis, because the layer blocks light.
That said, if your plants outside do look a bit mucky, there's nothing wrong with cleaning the leaves if you want to.