Rant: everyone says to keep a separate folder for each client, that's how you end up with 60 tiny folders and no system | Clutter-Free Workflows - The Design Community Hub
The bigger issue is that a folder tree assumes you know where a thing lives. Half my work doesn't fit one client or one project. That contract clause gets reused for three different clients six months later. A folder buries it. Tags and good search beat folders every time. One big pile with solid naming rules beats sixty neat little boxes nobody can search across.