Freebase was developed in the mid 70's to make cocaine a smokeable drug. Being an intermediate step, it still contains toxic chemicals such as kerosene and leaded petrol.
Smokeable cocaine is desired because it reaches the brain faster.
Next it is more fat soluble than snorting cocaine and so is more readily absorbed by the fatty brain tissue causing a more intense reaction. The lungs which are the transfer point for the smoke from the drug and the interior of the body, are composed of thousands of tiny air sacs located at the ends of the bronchi, the breathing tubes. The basic purpose of these microscopic structures is to put oxygen back into the blood. Freebase cocaine also mimics certain body functions such as sleep, hunger, thirst, or sex by its effect on the pleasure centre in the mid brain, that part of the brain which tells us when we've satisfied one of those bodily needs. If this was all that smoking cocaine did, if these were the only effects, it would be even more widely used than it is now and as available as cigarettes.