If you use depth map shadows, by default Maya calculates at least one depth map for each depth-map enabled light source and for each frame of the animation during rendering.
In some cases, you can reduce rendering times by saving and reusing a light’s depth map. See the following table to determine if reusing a depth map is advantageous for your particular circumstance.
Maya saves depth map files in the renderDate/depth directory of the current project, by default.