This control lets you switch between displaying maps as shaded (Phong) or realistic (full detail) in viewports.
(Material Editor): Compact > Show Shaded/Realistic Material in Viewport flyout
Compact Material Editor menu bar > Material menu > Show Materials in Viewport As
Main 3ds Max menu > Views menu > Show Materials in Viewport As
(Slate Material Editor: Toolbar > Show Shaded/Realistic Material in Viewport flyout.)
The control for showing maps in viewports is a flyout with four possible states:
Show Shaded Material in Viewport [off]: Uses Phong shading for objects that use this material but disables viewport display of the material's maps.
Show Shaded Material in Viewport [on]: Uses Phong shading for objects that use this material and displays the material's Diffuse Color and Opacity maps.
Show Realistic Material in Viewport [off]: Uses Realistic shading for objects that use this material but disables viewport display of the material's maps.
Show Realistic Material in Viewport [on]: Uses Realistic shading for objects that use this material and displays the material's maps.