For more information about shadows, see Shadow in Maya.
Removing unnecessary shadows can help reduce rendering times. You can either remove all shadows produced by a specific light, or all shadows cast by a specific surface. To determine which objects cast shadows, see Control which objects cast shadows.
To remove all shadows produced by a specific light
To remove all shadows cast by a specific surface
You can make all shadow casting surfaces cast shadows from all shadow casting lights, even if they are not linked together, by selecting Shadows ignore linking from the drop-down list in the Render Options section of the Render Settings window (Window > Rendering Editors > Render Settings).