What?
This mod lets you mix 2 fluids together which isn't that useful on its own since there are no recipes in vanilla requiring 2 or more fluids except advanced oil processing.
Why?
If you use the mod with the default settings it will create mixed fluids and barreling recipes. Those fluids are kind of denser then their ingredients so that barrels and pipes can hold/transport twice the amount of fluid.
But, why?
The mod is designed as a library so that modders can use it to create barreling and un/mix recipes with optional technology to unlock them in any data-stage.