For one, they act as air pollution indicators. Although a lichen is able to withstand harsh conditions, such as freezing, thawing, high light and heat intensities, when an area is polluted, lichens will become scarce and eventually stop growing. Lichens also help regulate the composition of gases in the earth's atmosphere. Each creature acts as a sponge to catch and store excess gases, one of which is carbon dioxide. In essence, lichens help filter the air we breathe.
Some lichen also have the ability to return valuable nitrogen to the soil.