People who think they have no authority may be surprised by how much damage they can do just by talking in an authoritative tone. See believing everything you're told and cached thoughts. A simple "YMMV" might be enough to prevent that.

"There's no problem with you" can have a lot of persuasive weight as a response to a comment about what may or may not be a problem with CronoDAS. All things being equal, choosing the option that makes you look better is a fairly common bias.

Also, your status as a member of the lesswrong community and your tone, implying you've understood his particular situation, both lend you a slight boost in authority above random-person-on-the-Internet. I don't know whether this boost is trivial or not, but I think Eliezer is proposing a general rule which, although it will overshoot its mark, will guard against biasing the advisee, even in cases where you'd think it wouldn't be an issue. I believe there was an OB article on these sorts of rules, but I can't figure out what to search for.