I've seen that advice elsewhere. I've always figured it was probably pretty rude. I mean, if an editor/agent asks you and you start with "Well, it's not really up your alley, but..." that's different. But if you are signing up for a pitch session, have a pitch. Even if you don't actually have a book, have a bloody pitch.

(Here we see why I could not do alg's job. Someone would say this to me and I would respond with "Then get out of that chair so someone who has something to pitch can talk to me." Probably not the first time it happened. Probably not even the second or third. But eventually? Oh yeah.)