Depending on the game, this could open you up to a perma-ban (if found out). Which I think most multiplayer games take a hardline stance against circumventing their rules.

I don’t know, if LoL uses it, but there’s some pretty ridiculous infrastructure in place for DRM, where programs can detect that your entire hardware stack (CPU → GPU → cable → Monitor) hasn’t been tampered with: https://en.wikipedia.org/wiki/High-bandwidth_Digital_Content_Protection

They still can’t detect when you’re filming your monitor, but pretty much everything else…