The wording for this paragraph is a bit confusing:

A feature that makes using Turbo Streams easier from the controller side is that Rails recognizes turbo_stream as a format in the same way it recognizes html and json. The Rails controller can then use respond_to. Within your respond_to block, Rails recognizes turbo_stream as a format. As a format, that means that you can use format.turbo_stream to specify response behavior specific to Turbo requests. Rails will also automatically use a file with turbo_stream as the format, the way it does for HTML and JSON, so it looks for a file named <action>.turbo_stream.erb. When Rails recognizes that the request is a Turbo Stream, it does not use the layout when it returns the response on the theory that a Turbo response will only be interested in the body part of the page anyway. This is a small but helpful performance benefit.

I suggest something like:

A feature that makes using Turbo Streams easier from the controller side is
that Rails recognizes turbo_stream as a format in the same way it recognizes
html and json. This means that you can use format.turbo_stream to specify response behavior specific to Turbo requests within your respond_to block. In doing so, Rails will also automatically look for a file named <action>.turbo_stream.erb. When Rails recognizes that the request is a Turbo Stream, it does not use the layout when it returns the response on the theory that a Turbo response will only be interested in the body part of the page anyway. This is a small but helpful performance benefit.