Since I sat the HSC for new syllabus subjects (Chem, Eng and Bio), I didn't do too many past papers for those. I bought the SUCCESS ONE Excel books 2019 Version for both Chem and Bio and did the entire thing. Helped me SO much for my trials and I topped my class in both subjects. For HSC, do the 2019 paper since it's out now (it's very different to the EXCEL style questions for Bio and focuses more on analysis of data rather than conceptual questions).
For English, I just did the questions and sample exams provided by companies such as Matrix, Art of Smart and ETA. I don't think I did a single past paper for English and I still ended up with a Band 6 (since it was for the new syllabus).
For Maths and Maths Ext I did as much past questions as I could since 2019 was going to be the last year for the current syllabus. I'm not too sure whether past papers are still relevant for 2020 and onwards but I'd check with your teachers and school for that.
For SOR1 I did every past paper from 2017 to 2001, some timed and some not-timed. Suprisingly, I got the highest HSC mark for SOR1 so I guess there is a benefit to doing past papers. But obviously this would vary between people. I advise not to do past papers unless you're 110% sure you know the syllabus back to front (or at least almost).