Plau Type & Design Booking.com is a good example with a crowded UI.
I’m not aware of any formal studies or experiments, yet. :)
However, I often see the trend that whenever there is a “discovery or exploration phase” involved, e.g. Searching for products, Search Results, News websites, and other information dense services — they all prefer to fill every inch of that white space available.
Most of these decisions are embedded in the data we collect from user behaviors. If users see a link, they click it (when in discovery/exploration phase). These clicks are directly tied to revenue. No one wants to lose money! Amazon, eBay, Alibaba.com, and other e-commerce giants all use this to their benefit.