I can kinda see the argument. Basically, it allows your club to react more dynamically to the way the draft pans out.
The obvious case: your recruiter is absolutely in love with player X but he is expected to go in the 10-15 range and you traded out your first this year so you don’t get to pick until #30. You tried to trade into the first round to get him, but nobody was biting. Come draft night when it turns out he’s still on the board at 20 - well, now you might be able to do something. You couldn’t trade up to 10 to grab your target,. but trading up to 21 might be much more possible, even though you didn’t try in trade week because you assumed he’d be gone by then.
Or: you really need to draft a key defender this year, and there’s a few good prospects. You had a high pick in the first round and picked up a mid as best available, and you planned to pick up a kpd with your 2nd rounder. However, in the early teens the defenders start getting snapped up one after the other, ahead of where you thought they’d go. Real concern you’ll miss out on all the ones you rate. You can potentially tray to trade up so you can fill your needs, rather than leave a hole on your list cos you misread the way the draft was going.
First problem i can see with this is that both my examples have teams wanting to trade up. Dreaming up a scenario in which they’d want to trade down is a fair bit harder. Which means it probably wouldn’t happen unless massive overs were offered.
Second problem is that clubs would have very limited currency to make these trades happen. If we restrict draft-day trading to picks rather than players (which is obviously 100% necessary, cos players should imho retain veto rights over getting traded to somewhere, and expecting them to make this sort of snap decision within moments on draft day is just not somewhere we should go), then most clubs have what, a couple of picks this year and a couple more next year to deal with?
Mind you, the WORST possible argument for all this is ‘it’d make the draft more interesting for viewers!’ Ye gods, even if this is true (which is debatable, most likely it’d be all “there will now be a 10 minute delay while West Coast discusses a trade offer for pick 25 behind closed doors, during which time we’ll have Brian Taylor and Basil Zempilas babble continually about the #1 pick cos he’s the only draftee whose name they know”) the purpose of the draft is to allow clubs to actually build a damn list. Careers and premierships and millions of dollars and, in some cases, the continued existence of a club, hangs on it. If you’re messing with that just to make it more telegenic, you should keep your hands off.