With the new nvidia cards already having 8GB it starts to seem meagre to have 16GB main memory on a system. However I found 16GB is about the sweet spot for having large amounts of RAM, since anything over tends to only be used extremely rarely. Basically only when editing HD video in after effects. All this is my experience on widows mind you, other operating systems might have other sweet spots.
On other side when you can get a DDR4-2133 16GB module for ~60 euros (and higher speed ones for just few euros more), getting even 64GB of RAM in just 4 memory modules does not sound expensive.
