For your safety, of course!

In fact, the sweep is to remove any deposit caused by incomplete combustion of wood. These residues are called creosote and soot. Both possess a combustibility, but in the case of creosote, its potential energy is higher than wood, so it is a highly flammable substance.

If this deposit catches on fire near the base of the chimney, it can cause a violent fire that, while making it’s way up the chimney, causes the temperature of the fire to get extremely hot and may damage the bushels of clay on masonry chimneys or the metal ducts of prefabricated chimneys.