Worm gears are used when huge equipment reductions are needed. It’s quite common for worm gears to possess reductions of 20:1, and actually up to 300:1 or greater.
Many worm gears have an interesting property that no gear motor for greenhouse various other gear set has: the worm can simply turn the gear, however the gear cannot turn the worm. This is because the position on the worm is so shallow that when the gear attempts to spin it, the friction between 
your equipment and the worm keeps the worm set up.
This feature pays to for machines such as conveyor systems, where the locking feature can act as a brake for the conveyor when the motor is not turning. One other very interesting utilization of worm gears is definitely in the Torsen differential, which can be used on some high-performance cars and trucks.