This rate measures how the temperature changes win the altitude. It’s extremely important because it lets you understand climatic changes. If the air cools faster than the lapse rate it will be colder and once it’s cool it will go down because of its density. This way the air’s in a ‘trap’ and won’t get upwards uncontrollably. And on the opposite, if the lapse rate’s higher the air will rise despite the cooling and this is what we call an unstable atmosphere.