Yeah, it depends on what you want from a document management system. If you've got a bunch of searchable PDFs, then storing them in a cloud service might well be sufficient. Paperless-NGX adds OCR to the mix (probably more useful for scanned paper images) and also tags. When I add a document, it fills in the best guess for correspondent, document type and appropriate tags, which tends to be accurate for common documents (e.g. payslips, statements) and usually only needs me to change them if it's from someone new.

What I find most useful is grouping together holiday documents such as travel insurance, holiday booking details, passports etc. and assigning a suitable tag, so I can easily find the relevant info. You could easily replicate that by copying those documents into a separate folder for easy access, but with Paperless-NGX it does most of the organisation for you and the search is more flexible as you can specify what kind of document you're looking for and who it came from.