The distance formula came to mind when thinking of a quick example of using flow. This might not be the best example of using _.flow, as the formal is simple enough where it could just be expressed in a single line. Never the less if you do not have much experience with _.flow this simple example should help give you the basic idea of why _.flow can be useful.
Maybe this method would be part of a framework, or just a stand alone method like this. However for the sake of this post that involves the use of _.flow this is an example of something that can be broken down into a situation in which a function is created that is the result of one function flowing into another. That is instead of doing everything in a single line, I could have a method that excepts the four arguments preforms a single step, and then passes the result to the next function and so forth.
Another way of producing the same method would be to use _.flow, by passing an array of methods to it. The first method in the array would accept the four arguments and return the product of Math.pow(x1 - x2, 2) + Math.pow(y1 - y2, 2). That product will then be passed as the first argument for Math.sqrt, and then its product will be passed as the first argument of Math.round.