The most obvious example of this is a compiler. It’s a basic task is to take some text (code in a programming language) and turn it into some executable form (e.g., object code for a specific hardware). Over time, we’ve found this can be usefully split into a chain of phases: tokenizing the text, parsing the tokens into a syntax tree, then various steps of transforming the syntax tree (e.g., for optimization), and finally generating the object code. Each step has a limited scope and I can think of one step without understanding the details of others.
