This can be aesthetic or functional or both, as it displays a particle effect above a cauldron and allows the player to cook food in the cauldron when fire or lava is placed under it. The max stack size and time for each item is configurable!!!
The particles are right above the water regardless of the water level of the cauldron. The normal function of the cauldron is not changed. This is just a small visual effect to make a server seem more alive. I saw a server place a cauldron above fire as if to heat or boil the water, but the water was just sitting there, so I decided to make the setup a little more interesting.
To cook food, throw the raw food into the cauldron (the max stack size can be set in the config - defaults to 1). The cooked food will come out after the amount of time set in the config (defaults to 8 seconds) multiplied by the stack size and the water level will go down. There must be some water in the cauldron in order for the food to be accepted into the cauldron.
Video Tutorial: https://www.youtube.com/watch?v=QsLr0RFjnEI