I really wish it were possible to calculate the total destruction of human productivity caused by whitespace and "progressive disclosure".
When applied correctly, all the term really means is thoughtful, research based surfacing of features, taking into account target audiences and the way features relate to each other. It’s why you don’t just dump all your features into the main window of your program, turning it into a Great Wall of Buttons. Thoughtfulness is increasingly uncommon though, UI design has more and more been treated as generic visual design instead.
It also serves as a key shortcut cheat sheet which is important for cultivating a fervent base of power users for your app. Maintaining a knowledge base article of shortcuts is probably good enough for existing power users, but it won’t grow that group nearly as well as menus can.
As always, design should be based on fundamental principles of human biology.