Much like simulated fire effects 3D simulated liquid effects can allow you to maintain control and the ability to edit that you simply would not have shooting in the real world.
Realistic liquid dynamics can be recreated to show accurate water flow through pipes. Syrup poured over pancakes. Ice cubes dropped in a drink. Waves crashing against a 3D object. Pirate ships at sea. Liquid pouring to form a logo.
Cartoonery Studios can create simulated fluids that can be controlled and used to create things with liquid that would be either very difficult, or simply physically impossible to shoot practically.