There is certainly no shortage of GCSE past papers, but it all depends on how you feel and how far through the course you are. If your exams are close, then there's no harm in doing them as exam technique is going to be pretty crucial, especially in essay based subjects as you say. I'd argue often more so than actually knowing the content in some cases. However, if you can afford to go over the content again, it would be more beneficial to do them once you are more familiar with the content, as the recall as you are doing them acts as its own revision. Obviously, if you are well and truly clueless as to how to go about answering something, don't hesitate to refer back to textbooks/notes/videos and whatnot as sitting and writing down semi-coherent waffle for 45 mins is not effective use of your time (nor is it fun)