When You Minimize 3ds Max While Rendering

Minimizing 3ds Max while a CPU render runs frees up a small amount of resources used to draw the viewport and render frame buffer, which can give a marginal speed boost on long jobs.

For GPU renderers the effect is negligible, and hiding the frame buffer can occasionally cause display glitches when you restore the window.

The reliable way to free resources is to render through a command-line/batch process or a render farm, which skips the UI entirely and is far more stable for big jobs.