The Case component dialog selects an envelope for maps presented on member structures, slabs/shells, or volumetric structures. Select a few load cases and either click (Select Case Component) or select Loads > Select Case Component to launch this dialog.
Choose the envelope (top or bottom) of a quantity picked for the selected load cases. The top or bottom envelope is presented for maps displayed on member structures (only for maps on members), slab/shell, or volumetric structures.