iloco; That option should really be called the 'background redraw' thread, because that is essentially what it does. That is the screen refresh for the non active components in the viewport, and any effect that changes in your active component(s) might produce (such as shadows, or hotspots caused by adding light sources). It also handles the realtime redraw whenever you actually move something; that is why you disable the feature whenever you have the trouble of creating an object, moving to a new location, and you get multiple ghost artifacts of that object along the path you moved it. And the big kicker is that this thread uses (I believe )your video card to handle the redraw; disabled, the task falls back onto the CPU.