Ah I've definitely wondered about this, but have not come to a conclusion either.

On one hand, I'm not sure it'd save much time. Randomly glancing through people's pages, I see lots of "No post links found". It seems like most people don't POSSE most of their posts or don't include backlinks on most of their posts... But it does seem like a good heuristic in general. The only case where it would lead to an "incorrect" result is if someone posts a message with a link to another, older post, which I'd guess is quite uncommon.

My vote would be keep it in mind if posse-post-discovery turns out to be costly.