From Facebook Developer Wiki

There are two extended permissions that apply to the stream:

• read_stream
• publish_stream

Contents 1 read_stream Permission 1.1 When Do I Use It? 2 publish_stream Permission 2.1 When Do I Use It?

read_stream Permission

The read_stream permission lets your application or site access a user's stream and display it. This includes all of the posts in a user's stream. To get a user's stream, call stream.get or FB.ApiClient.stream_get.

When Do I Use It?

You can prompt for the read_stream permission if you want to show the user's stream or the user's friends' streams. This was designed for use in alternate Facebook clients, such as Facebook for Adobe AIR.

publish_stream Permission

The publish_stream permission lets your application or site post content, comments, and likes to a user's profile and in the streams of the user's friends without prompting the user. This permission is a superset of the status_update, photo_upload, video_upload, create_note, and share_item extended permissions, so if you haven't prompted users for those permissions yet, you need only prompt them for publish_stream.

If the user grants the publish_stream permission, then your application can publish stories on the user's behalf via a call to stream.publish. Without the permission, that call will fail.

When Do I Use It?

You do not need the publish_stream permission to post a Feed story. In most cases, it is a better user experience to display a Feed form (rendered with Facebook.streamPublish or FB.Connect.streamPublish), asking whether the user wants to publish the story. This leaves control over the individual story in the hands of the user.

However, you may want to prompt for the publish_stream permission in the following circumstances:

• Your application does not run on the Web, like a mobile or desktop application. Or an application that runs on a gaming console and may not be able to pop up an IFrame to prompt for the permission. For example, see Facebook for Adobe AIR.
• Your application performs activity when the user isn't on the website. For instance, some applications accept content via email or text message. For those apps, it's not practical to show a feed form.
• Your application performs an action repeatedly, making the user experience awkward if it gets disrupted by Feed forms. For example, syncing a user's status from another site with Facebook.

If your application executes on the Web (as most do), and the user sends Feed stories only for important actions, then you may not need this permission.