Registering an app and adding the client ID into requests just takes a few seconds, and one of the reasons it’s needed is in cases where if for example your site did these requests client side and had a flood of users, or malicious users, or some sort of bug that caused excessive API requests, Twitch can easily see by the client ID on the requests who to contact to resolve the problem.
As tduva mentioned, you don’t even need to touch OAuth unless you want to use API endpoints that require authentication .