What's the difference between a tiered letter tray and a vertical file sorter?

Tiered letter trays (horizontal slots) work best for loose paper, mail, and documents you handle daily, since each tray holds a small stack flat. Vertical sorters stand folders, binders, and notebooks upright like books on a shelf, which is better for project files you grab and replace often. Most desks benefit from one of each rather than two of the same type.