Granting “Publish to stream” permissions means you’re giving permission for that application to post events to your news feed. For example, if you granted it to a running application, and you used it it might make a post that said “chaosrob ran a mile!” and your friends would also see that in their newsfeed. Fluther asks for this permission so we can publish when you ask a question (but we’ll always ask you before we post to your newsfeed on a per question basis).