The "computer" part is required to install highly recommended add ons for game mode that improve overall deck performance. It's also required for when game mode starts acting off, like when sound suddenly stops playing, for example, or when a game won't run in game mode and needs tweaking. If you want to emulate your games from other consoles, it is also required to maneuver. It's also required for when you inevitably want to start modding your games to get the most out of them. Sure, you can totally avoid it if you want, but you will eventually have to use it. "Decky Loader" is another good example. It unlocks the steam decks potential in many ways, but you need to use desktop mode to get it working in game mode.

What an odd thing to downvote lol