On low quality video settings, only 25 Rain Clouds will produce rain in an area. On medium quality, 112 Rain Clouds will produce rain. Additionally, the rain starts fading sooner on lower quality settings.
If the block is made inactive via an Actuator, the rain animation will still be there.
A solid block underneath a Rain Cloud stops the rain from falling, while a hammered block does not.
Small pools of water usually generate around these blocks.
The rain effect helps locating Floating Islands.
Rain Clouds can be used at the bottom of Hellevators to avoid dying from fall damage.