What is the use of the spermaceti organ of the sperm whale?
One possible theory considered is that it was used for floating and going underwater by heating/cooling the oil. However, it is a lot easier for this to be done mechanically.
Another possibility is that it is comparable to a helmet to safeguard it when it collides with another whale. However, other animals have much simpler structures to deal with this problem.
A third possibility is that it uses it to stun its prey like squid. However, research in inconclusive on whether squids can hear or not. The link below, says that it is probable that squids can only hear upto 500 Hz which is not the frequency used by whales, thus this theory is probably false as well.