that's the obvious issue. another less intuitive one is that modern cpus and compilers are essentially optimized for iterative algorithms. state variables can b

that's the obvious issue. another less intuitive one is that modern cpus and compilers are essentially optimized for iterative algorithms. state variables can be kept in registers, simd can be used for data that appears in contiguous arrays, caching is built on locality assumptions and data locality is preserved. non-flattened recursive algorithms spread their state across linear memory with a full stack frame for every iteration. at the least this defeats gains from caches, at worst it defeats them entirely by filling them with junk. but, if the problem is small enough it can be worth it for the correctness guarantees and increased simplicity. trivial iterative algorithms are simpler, sure, but when things get more complicated, recursion can replace very hard to understand, test and debug iterative code with simple recursive definitions where guarantees of correctness and termination come for free.