In brief: Twitch released a native app for the Nintendo Switch this week. However, the service doesn't integrate into the platform as well as it does PlayStation and Xbox, and the features are limited compared to the PC version or website. Still, this increases the small but growing number of streaming apps for the Switch.
The Twitch app on Switch doesn't let you host a stream. Sharing your gameplay or posting clips isn't integrated into the Switch like it is into PlayStation or Xbox (though the Switch does let you share screenshots). Instead, it's just for watching Twitch channels, and it does get the job done in that regard, with functional browse and search tabs. Of course, the video quality is as good as it can be on the Switch's 720p screen.
Other than the lack of hosting streams, the only other significant limitation in Switch's Twitch app is that it won't display streams and chat windows simultaneously. The chat will appear on a streamer's page before you start watching, but engaging while viewing a stream requires using a mobile device. However, the app does let you use QR codes or an activation link to make logging in smooth.
It is somewhat silly that chatting while watching a stream on the Switch requires users to log into a mobile device's installed Twitch app. Since Twitch for iOS and Android already allows chatting while viewing a stream, it raises the question: why not simply watch on mobile?
The only advantage of using the Switch and mobile together that I can think of is that it might offer more screen real estate if your mobile device is a smartphone with a small screen. Splitting the two into separate screens might be more comfortable for some.
The Switch doesn't have nearly as many streaming apps as the other consoles, but it does have YouTube, Hulu, and Funimation.