Having been there fairly recently myself, I can relate to students and likely remember asking myself the exact same questions

I'm currently a 2nd year Chemical engineering student at the University of Edinburgh, meaning that I've pursued biology, chemistry, maths and physics since the start, beginning with grade 9's in these subjects at GCSE level (I'm from England), onto four grade A's in sixth form.
Understanding for me makes all the difference, meaning that I like to go above and beyond the exam specification so that revising doesn't feel like relentless memorising. I'd bring this approach with me in my tutoring; starting at any level, we can work together to accumulate that higher level understanding