Well, for Ctrl+F there is sometimes a reason. Many websites uses technique called virtualization of lists. That boosts performance, but standard Ctrl+F doesn't works anymore properly
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..
Really i see no valid case
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???
github code editor is a big one
The good sites allow you to hit ctrl f twice to get browser's find feature.