At first glance, there doesn't seem to be any difference between Turbo frames and Turbo Streams, other than Turbo Streams let you stream live updates via WebSockets.
However, the really cool thing about Turbo Streams is that they let you target and update multiple, unrelated parts on your page in one response. This lets your application REALLY behave like a single-page application. In comparison, Turbo Frames only allow you to target a single element (frame) at a time.
Another big difference between the two is that Turbo Frames can only let you replace the existing frame. They won't let you append, or prepend to existing content. You can't remove any elements on the page as well.
Finally, a common misconception regarding Turbo Streams (I used to think this, too) is that it can only be used with WebSockets to send live updates. This is not true. You can use it on POST requests after form submissions or button clicks to update multiple elements on your website. You can also use them on GET requests via link clicks.
In a nutshell, Turbo Streams allow you to target multiple parts on the page, and also let you append to, prepend to, or remove existing content. No WebSockets needed, either!
Should You Use Turbo Frames or Streams?
Turbo Frames are great when we want to divide a page into independent components that can be updated on their own, without impacting the rest of the page.
In contrast, Turbo Streams are useful when we want to make multiple changes to multiple elements on a page with a single request, e.g. form submission or button clicks.
As a general rule, start with Turbo Drive, which you get for free. When you need more interactivity, use Turbo Frames. Finally, for the last bit of interactivity where Frames aren't enough and you truly want to make your application come to life, use Turbo Streams.
This is what I love about Hotwired approach to building web applications. You don't have to go all guns blazing for your simple website that just needs to render a few pages. You can enhance it progressively, using advanced tools only when they're needed.
This wraps up our brief exploration of Turbo Streams. I hope you have a better understanding of the use cases for Turbo Streams and how they differ from Frames.