The idea behind Opera GX is to provide players with a way to surf the Internet while leaving available computer resources to the game or live applications running at the same time. Running a game requires a lot of computing resources, and if you stream it at the same time, you will need more resources. In order to reduce resource usage, players usually close the browser before the game to prevent it from affecting the game experience.
Opera says that with Opera GX, players don't have to close their browsers. In addition to limiting CPU and memory usage, Opera GX also integrates the live game service Twitch.