Wray Scott recommends that we simplify our drawings' background details during animations.
"When creating animation, it is not always advantageous to have a complicated background, because it will increase the file size and rendering time. This is a time to heed the saying 'Less is more.' Simplify the detail in the background, and you can have that much more detail in the things you really want to show off. Keep it simple when you can, especially if you only need to make a rough draft of your animation."
Notes from Cadalyst Tip Patrol: AutoCAD can't do much in terms of animation: you can only have one camera move along a path. Regardless, it takes time to render each scene in the animation, and the longer your animation, the more work there is for the computer to do. Every frame has to be rendered, even if you are not applying materials. If you are filming at the typical 30 frames per second, for 30 seconds, that means AutoCAD has to render 900 images. If it takes 10 seconds per frame (for a simpler model) then it will take you 150 minutes to create this animation — that's two and a half hours!