When programs take advantage of it. The only time I've ever seen a need for 32GB in my machine is when I was working with a ton of really high res scans in CS6 and it kept all that data in RAM. I haven't ran CAD or anything on it, but I have done some movie editing and it didn't take that much. 95% of all tasks can be accomplished easily with 16GB, and gaming can still be easily done with just 8. I'd say the most I've used my RAM for is RAMDisk for Skyrim.