That is surprising to me, but more pertinently, how often is this the case? Even if expectations don't match, how often do you actually undercut the recruiter's expectations? I would think most people would have a reasonable ballpark idea of what the recruiter has in mind - so just overshoot and then get negotiated down from there. The suggested tactic only really makes sense to me if you frequently expect to be undercutting what the recruiter's got in mind, and even then by a lot.

To my layman understanding, the larger the difference between expectations, the lower the value in this tactic of not revealing your expectations.

Young engineers often undercut their value by a lot. That's part of why they are popular

I agree (and expect) that people new to the job market would be poor estimators of their market value. They would also have the least room to negotiate.

True. juniors dont know their market value and that makes it easy to get them stuck in low-paying jobs