My thought on it is I’ll spend way more time learning how to do it on the calculator than is worth it, and be 25% less sure on my answer and have to do it twice on the calculator. Rather do it on paper.
Well, it all comes down to personal preferences, right? I make far more mistakes by hand than with my calculator. And I prefer to save some time on the calculations, since time is an issue during the exam. But if you don’t master your calculator there is really no point - especially a week before the exam!