Chimneys need to allow the free passage of dangerous combustion gasses. Regular sweeping will remove soot, bird nests and any other blockages. It also removes creosote, which will help to prevent dangerous chimney fires. Chimney Sweeping will also increase the efficiency of some appliances.
The main benefit from having your chimney surveyed is the flue is a hidden part of your property that could cause serious risks to health. If you have not used your chimney in a period of time, have moved into a new property also if there has been a chimney fire we highly recommend an inspection to determine the condition of the chimney.