If you use Reddit and do check it's data usage, you know what I am talking about. There are a few posts on Reddit itself but want to know from developers who either work at Reddit or those who have gone deep into these issues.
Thanks.
You can kind of answer your question by opening up your browser's developer tools and looking at the Network tab which shows you every request made, it's destination, size, duration, etc.
They're a data hungry tech company like any other tech company worth its salt these days. The reason it's free is because the data on its users is so valuable. They've monetized it in any number of ways.