I know of 2 websites that do this.
1. Confluence
It's super annoying and takes up a lot of screen space
2. Nexus
It simply kills it. You can use ctrl-f but it simply will not find text right in front of you..
DOS emulator and Vim emulator, and that's almost all I can imagine. Maybe games that would use the control key as an additional input---but in the browser???
Really i see no valid case