An empty account leaves a strong impression of "This user came, wrote a stupid comment, got downvoted into oblivion, deleted that comment and never came back"

Or they created an account to reserve their name, but never used it. I vaguely recall there being services that will automatically create accounts for you on many sites at once, to prevent other people from using your name. Which means that if you generate publicly-visible evidence that you've used one of those services, then having empty accounts will no longer reveal anything. (People would have to notice that you'd done that, of course, but someone would have to be extremely detail-oriented and interested in you specifically to even notice that you had an empty account.)