Commercial, large scale cannabis plantation require a number of mature plants to be processed in a short period of time, just when the flowers become most potent marijuana. Separating flower buds from the leaves and stems would take long hours - that is where automatic, mechanical trimmers come in.
These devices vary in a degree of work done, but the basic principle is to put a whole cannabis plant inside, and take out pure weed. The smallest and simplest ones are mechanical, with a set of sieves working as a separating agent.
More advanced machines, offering much higher output, run either on electricity or gasoline. These professional devices should be operated in full protective wear, i.e. at least gloves and some eye protection. Precise and delicate handling, yet at great speed and efficiency - just what large scale cannabis producers need.