@Six Assume you aren’t trying to cheat a system. Let’s say you’re making a mobile phone app. You make one client-id, and the user auth’s their own account for usage of the API. If it’s by IP Address they cannot hurt other users. If it’s buy client-id then one user can destroy your app for all users using the app. Limits by client-id do not scale. Limits by IP at least scale somewhat, albeit limited to the functionality you can supply.
Being caught using 10-50 client-ids can get you perma banned on some API services once they realize you’re using multiple client-ids.