Pollution, dust, smoke, vehicle fumes will all cause your asset to become soiled. This will spoil its appearance and hide any patterning/detail.
Plants and seeds which grow between jounts in paving or slabs can lifting of the blocks and also allow more water to accumulate underneath causing subsidence. In severe cases the block/slabs may crack requiring replacement.
Lichen, moss and algae can all contribute to a sluppery surface on the drive/patio/decking.
Slips and falls can cause injury and possible loss of income especially in wet weather.