Brian,
You're the cap expert, but I believe this to be correct.
Trading for a 1st round pick automatically comes with a cap hold. 2nd rounders do not. So, we can use our cap space and then sign our 2nd rounders. We would have diminished cap space if we traded for Gobert (or anyone else) in the 1st round.
You're right, but not exactly. Yes, the 1st-rounder comes with a cap hold. It's about 900k for the 27th pick. But it takes up one of the "roster hold" spots (that are 490k), so you're losing 400k in cap space in order to guarantee a guy on basically a 4yr, 5M total deal--with the ability to cut him loose after two years like Nolan Smith if he really sucks and you don't want to pay 1M/yr for him. And the 2nd-rounder doesn't cost anything in cap space, but you can't sign him after you've used your cap space unless you use one of the exceptions. Rookie minimum is 490k. You could use our Room Exception to do something bigger, but only on a 2yr max deal. IN which case you end up getting Lin'd (or Asik'd) if he turns out to be good, and if he sucks you've only spent less than 1M total over the 2 years that would've been guaranteed at #27 (or whatever)
So if we would've traded, say, #40 and $2M for Crabbe at 27, then we could've a) kept our future 2nds, b) locked Crabbe up on a guaranteed 2yr 1.9M TOTAL deal, with team options for year 3 and 4 at about 3M total if he's worth it, c) avoided an "Early Bird" situation like Lin and Novak---at the cost of 400k in cap space and 4M or so in cash.
Of course, we could trade for them later, but it doesn't sound like that is in the works.
This is one of the great things about the #31 pick. First, you aren't locked into the rookie salary scale, so you can get a Euro who has a big buyout (teams can only contribute 575k to a buyout, player's on the hook for the rest). If you could, say, offer a guy with a 2M buyout the MLE (or some portion of your cap space), then you have a much higher chance of bringing him over than if you draft him #27.
Second is if you want to draft and stash a guy and keep him off your cap, then a 2nd is the way to go b/c you have to have a first round stasher sign that he won't come over in the following year (even in trade). Guys like Schroeder, Karasev, Adetobunbo didn't want to do that, so teams like DAL didn't want to draft them if they weren't guaranteeing that, or else the cap hold would still be on their contract.
My personal philosophy on end-of-first/beginning of second is that you should draft role players or red-flagged guys (or guys who've dropped) with late 20's picks, which are usually available for cash (or 2nds), and get expensive-buyout Euro talent with #31/32/33, so that you can keep them off your cap books while they're stashed and still maintain the flexibility to pay them enough to overcome a buyout.