The point is that it can complicate analysis of a program, at least if you take the fundamentalist view that all program behaviour should be provably correct. L

The point is that it can complicate analysis of a program, at least if you take the fundamentalist view that all program behaviour should be provably correct. Like if you need the collantz sequence of a number or something in your program, you would just calculate it and use it, but it's surprisingly hard to prove that it always exists. Which isn't so much a problem in itself as it complicates trying to prove anything else about your program's behaviour.