Virtualization is one that I frequently do. Running a VM to test out programs (especially to test out Windows compat, or macOS if you're feeling up to the challenge). 16GB can barely run an additional VM, and if you have 30-40 FF tabs open, an IDE, and so on, then running with just 16GB of memory becomes very restrictive. Allocating 8GB to the (one) VM would leave you with 8 for the host OS, of which 2GB is going to be used by the kernel/WM, and leaves only 6GB to develop with.