This tactic is widely used in especially 2v2 multiplayer games,because at 1v1games the enemy can blockade the Zealot army at the cliff and eridicate them easily by the role of high ground.But in 2v2 or 3v3 games the allies of the Protoss who made Zealot rush will help to protect from the damage comes from high ground effect and the allies may open the cliff with the concentrated firepower against the rival forces of the cliff entrance.When the defenses has been broken the Zealots will attack to the enemy resource location or production center.Here the choice is important if you are afraid of the enemy ally forces, you can directly attack the resource area and harm the enemy economics but if you want to end game immediatly you can attack to the enemy production buildings and stop the force development of your opponents.