Perhaps you don't care about the $100 fee. But if you do (as one might if it were a personal rather than business ticket), there is nothing to be lost by waiting until the last moment to cancel, and there is something to be gained: there might always be a schedule change, which if sufficiently large, makes the ticket entirely refundable, with no fee. There are many threads here about what is "sufficiently large" -- but experience shows that even small changes can sometimes be negotiated with a phone agent for a full refund. YMMV