When you turn on Progressive Display / Adaptive Degradation , 3ds Max can change the way it displays objects to keep up with the current operation. For example, while you are zooming a viewport, some objects might change from shaded to bounded boxes during the zoom operation, and then switch back to shaded display when you finish zooming. The settings on the Adaptive Degradation panel of the Viewport Configuration dialog control how adaptive degradation occurs.

When Adaptive Degradation is off, viewports retain their display settings at all times, but operations such as zooming or animation playback cause a slow screen refresh rate. In this state, animation playback might have to drop frames to keep up with real-time playback.

You can set the parameters that control the trade-off between display quality and display speed. The levels you activate determine which rendering levels 3ds Max falls back to when it cannot maintain the desired display speed. You can choose as many levels as you want, but for best results choose only one or two levels.