I was in the review queue today and I saw something strange:
comments disabled on deleted / locked posts / reviews
Is this a glitch, or something new? If it's something new, won't it be hard to leave constructive feedback for new users?
I'm not clear exactly where you saw that in the interface, but I don't think it should be a significant problem... I'm really curious what question it was on.
Deleted and locked are quite distinct from closed or "on hold". This shouldn't get in the way of leaving constructive feedback for new users.
I think you have to have over 10,000 rep to see deleted posts. We only delete things if they are judged to have no value. Unanswerable, closed, and not changed in months; completely off-topic; etc. For a question to get deleted, it either has to be entirely off topic (spam), or have spent quite a long time in a closed state waiting to get fixed.
Locked questions are quite rare. I think duplicates and questions migrated away from the site show up as locked. Moderators can lock questions, but we've generally only done it for questions that didn't meet our current standards, but that (for some reason) we didn't want to actually delete. Might get used for an hour or so on a question with a lot of off-topic comments.