Of course they're not the common case, but the parent wanted examples where they are used in calculations that do have nice answers.

So they are useful. They are more useful than most people realize that simply assume they only mark errors.

And without them in your case, you would not be alerted that a calculation went wrong. So even there they are very useful. Not using them correctly is like ignoring file API errors in your programs - sure they are rare, but you need to understand and handle them if you want to make good software.