With the same size of paper loaded into multiple trays, you can make the machine use one tray for one function and another tray for another function.
For example, you may load white A4 paper into tray 1 to use when making copies, and yellow A4 paper into tray 2 to use when printing received faxes. You can then easily identify for which purpose paper has been output. You can perform this setting in “Paper Tray Priority: Facsimile” in “System Settings”. See “System Settings”, General Settings Guide.
When a different size of document from the priority tray is received, the tray containing the same size of paper as the received document is used.