I am paperless and I keep for 7 years. Some important "permanent documents" are retained until I no longer work with the client or 7 years after last bit of work completed. I do not rely on tax software for data retention since I have had data become corrupted. Even with backups--cloud and local on rotating basis--it is simpler to keep PDFs for reference unless I need to see more detail within the tax software.
I do retain all documents used for tax prep, and I do occasionally refer back to them. Clients would find it annoying if I did not, but I am now scaling back to ONLY the documents that needed to be reported on a tax return. If it is informational only and not reportable, I am not going to keep it.
So, my overall suggestion is go through your documents. Identify what you need to retain by law, what you should retain for your benefit and good client relations, and then scan only those documents.
I was looking to buy a CPA firm that has been maintaining mostly paper records. They claimed to have a 7 year retention policy but when I was in their file room, they had boxes dating back to the mid-2000s. I knew that if the sale went through, I was going to have to hire dedicated staff just to convert all of that crap to electronic format. Glad it fell through, actually, because that would have been a horrible task!