[burger_moon]

For a non-nefarious use case, it can be used to iterate on the UI to create a better user experience because it can expose areas that people aren't seeing on the webpage. Your site might have the important content or useful navigation in a place that users aren't noticing which causes them to leave the site in frustration.

[seba_dos1]

Yeah, basically this. The data was aggregated and a graphical heatmap was displayed on top of the website, with some fancy accomodation for responsive designs. You could see heatmaps for hovers and for clicks. Customers then optimized their shop flow, adjusted graphics that looked like they were clickable but weren't, moved important content into more visible places, etc.