There are a few things that you must be aware of when rendering animations, that relate to the Mental Ray global illumination system.

You will probably be using final gather (FG) and global illumination (GI) when rendering your animation(s).

You can use ‘cache files’ that store FG and GI information between frames; this will save you significant amounts of render time, as well as reduce rendering artifacts. Read here

In this 3DS Max tutorial, the author is going to do a coins stack. It’s hard to keep accuracy when we want to do that manually because of lots number of objects. So it is quite smart to do some simulation.

Read full tutorial here