yeah, it's actually proven to help people in exams especially in the case of over anxiety and mental blanks/breakdowns, haven't you found sometimes (more common in maths) that there are parts that you can do normally with such great speed, but you spend more time on certain sections that aren't too hard, by talking to yourself this ultimately establishes an objective which you can clearly work through step by step to achieve your answer (especially necessary for maths)
I don't speak it out aloud in the exam lol, but I do mouth it, or whisper it very silently or without a sound, especially when I'm trying to rememorise things, this correlates with my memory, because through study of key factors for exams that require a lot of essays, legal, eco, modern and english, I usually remember my info by saying it out loud in a certain order anyway, so in the exam by saying it out, helps stimulate all those past hours of practice I've had ultimately maintaining my level of optimal arousal as well as putting down massive amounts of content.