Worm gears are used when large equipment reductions are needed. It’s quite common for worm gears to have got reductions of 20:1, and even up to 300:1 or greater.
Many worm gears have an interesting property that no additional gear set has: the worm can certainly turn the gear, however the gear cannot turn the worm. That is because the position on the worm is so shallow that when the gear attempts to spin it, the friction between the gear and the worm keeps the worm set up.
This feature is Screw Air Compressor useful for machines such as conveyor systems, in which the locking feature can become a brake for the conveyor when the motor is not turning. An added very interesting use of worm gears is definitely in the Torsen differential, which can be used on some high-performance cars and trucks.