Exams can be an extremely daunting time for students regardless of their ability and skill levels. Revision is proven to help improve your chances of passing exams and allows you time to revisit topics that may have been taught a number of months ago to refresh it all in your mind.
Some people plan their revision in weeks if not months ahead of time. They will work out all the subjects they need to revise for and split the revision period up in to blocks for each subject. This can take quite a bit of planning time but can often mean that you make sure you fit all the revision in. Other students prefer to pick and choice when they do their revision and what subjects they revise for. Often students will leave revision until the last minute. This is often not advised by schools or the education department but for some students it still can work well for them and is definitely better than doing none at all.