Why it's not too late
1. Because Every Little Helps
Deciding to "not bother studying" because it's too late now and there's "no point starting" is a huge mistake. Even if it's 3 days before the exam, you can still fit in some extra pieces of info into your brain that could make a difference in your test.
Say you have 3 days left before exams, and you use those days to study one topic in Life Sciences. In the exam, that topic comes up; even if you couldn't answer anything else very well, at least you have one thing that you're going to get high marks in.
This can be the difference between gaining a higher mark, so never ever resign to doing completely nothing.
2. Because you can't underestimate your brain
Your brain is amazing, and its possibilities are endless. Don't underestimate what it and your memory can do in the short space of a few days or weeks.
Take care of it and use it well, and it will help you out in return while you're studying and doing your exams.