I currently have 4 tabs open in Firefox, a couple of word docs open, Mail, Outlook, calendar, Messages, and a pdf document.
I also have Dropbox, Avast, a couple of text formatting apps, and Google Drive open. And I use 10.26 GB.
This is fairly minimal for me as far as when I work. My "typical" usage as I open a couple of more work apps, I use around 12.50 GB.
I've tried to get below 8GB, but I've found it hampers my ability to be productive as my work requires me to move between various apps (none of which are demanding apps in and of themselves). (I'm on an Early 2013 15" MBP).
Sure, everyone doesn't need 16GB. But it's easy to imagine a world where 8GB is not enough.