Absolutely agree with @3ventic. Caching is highly recommended when using pretty much any API. 
Showing online and offline users through the API has a lot of implications. I could see a bad actor creating a master list of all users on Twitch and then cross-referencing that with any of the multiple password leaks online. Or maybe the list finds a pre-launch channel and spoils a reveal. Showing online only means that someone is deliberately broadcasting, and you have access to their live content.