Fact 1: If you attach a plan to your ‘A’ level essay, Cambridge will look at it.
There are two possible outcomes:
1) Your essay was far better than the ideas in your plan suggest
2) Your plan suggests that there was a deeper, more thorough consideration of the question that your essay showed.
Either way, you win – in the event of (1), your plan will be ignored – after all, that was a draft and what matters is your actual essay. In the event of (2), you cast yourself in a better light, you appear cleverer, it might even make the examiner go back and re-read your essay in light of certain ideas in your plan, and if there were some excellent ideas in your plan that didn’t appear in your essay, you might get the benefit of the doubt that you simply ran out of time – and if the examiner was toying with a range of marks (common), it increases the propensity of them giving you the higher end of the range they were considering.
So, always do a brief plan – copy the question on a new sheet of paper, and scribble your ideas – just point form, use arrows and questions and show how you’re branching out from the key words to brainstorm scope. If you have any insightful comments/questions, write them down, circle them to draw attention to them – whether or not you end up using them in your essay, show that you thought about them. And when you plan, always attach the plan to the back of your essay. After all, there’s nothing to lose, and there’s something to gain.