It won’t make you perfect.
It won’t mean you’ll get no corrections.
It won’t mean you’ll be blank-free in the viva, or that it’s impossible you’ll be stumped.
It doesn’t come with anything like a guarantee.
But it means that, for a small investment of time, you are as ready as you can possibly be to meet your examiners and talk about your work with them. You’ve taken the time to boost yourself, not better yourself. You already know everything you need to know, you can already do everything you need to do.
This is the stretch before the race, or checking your lines just before you walk on stage.
The little extra that helps you get the viva done.