SF Signal: Mind Meld: The Tricky Trope of Time Travel

At SF Signal's weekly panel discussion, Mind Meld, this week's topic is: The Tricky Trope of Time Travel. Paul Levinson, Maureen Kincaid Speller, Gwyneth Jones, Ted Chiang, Robert Charles Wilson, Veronica Hollinger, Robert Reed, Paul Graham Raven, Tom Purdom and Stefan Ekman discuss these questions: Time travel is one of the trickiest SF/F tropes to use well. Why use it at all? What stories have used it to the best effect?