It is a special type of curried function that can only combine functions with a single argument and a single return value. It enables "unary programming."

It takes two functions, f and g, and creates a new function that applies them from left-to-right (f then g). It enables a style called "function chaining."

It is a debugging tool that logs the input and output of a function without changing its behaviour. It enables a style called "transparent programming."

It takes multiple functions and runs them in parallel, merging their results. It enables a style called "asynchronous programming."

It takes two functions, f and g, and creates a new function that applies them from right-to-left (g then f). It enables tacit or point-free style programming.