Suppose your company is developing a framework for creating mobile apps. You work on optimizing the GUI renderer and you are assigned a task to make a module which finds computationally equivalent render functions (or a company making a programming assignment plagiarism system, or a duplicate config file detector when the config language is accidentally Turing-Complete).

You may try removing whitespace, finding invariants, ordering the variables by type, converting for loops to while, tail call optimization, but your collegue always has a trick to make equivalent functions undetectable by your module. You were solving the halting problem. Instead, you should use CS knowledge and tell them it's impossible but they can have a non-optimal search. Perhaps, the fastest way to complete the task would be to score similarities between the functions' machine code or AST.