Sure, there's always just someone else you could pick. But if you trade down from 21 to 30, just to pick up a late 2nd, and then miss out on the guy you want, so you just grab someone else seems stupid to me. Well, we really wanted Nolan Smith, thought he was BPA, but had to go to our 5th choice, because we traded from 21 to 30, thinking or hoping he might be there, because that's what the mock drafts told us, and now, in between 21 and 30, not only did he go, but our top 4 other choices. So then, we're going to reach for someone at 30, and fans will whine and bitch, because they saw a mock draft say he would go later.
I understand the trading back and getting value. It's great if you can do it and still get your guy. It's stupid late to move too many picks back, not knowing if your guy, or your next 4 guys will be there.
Like I said, I think mocking the lotto is a little easier. So trading back from 5 to 8, knowing who is going at 6 and 7 is good. 21 to somewhere like 30 is a lot more risky, and foolish if you like a guy, for what amounts to not much value in return.