Some topics, like a call-for-bug-reports or a new Howto, will receive a lot of replies that go stale shortly thereafter because the appropriate fixes/edits were applied as a response. When closing or marking as solved doesn't make sense, the best solution to date is to delete these replies. Topic summaries offer a less destructive solution.
A simple way for moderators to insert pre-written responses to common inquiries. Reduces repetitive actions, especially in support-centric communities.
See who - apart from yourself - is using the "Reply" dialog box to write a reply to a particular topic. Targeted primarily at private group messages.