What happens (or what has happened) when the GM and HC don't agree? Being on the same page doesn't guarantee they are going to agree on every single personnel decision. And forming a consensus doesn't necessarily mean making the best decision. This was a worry I had with Reese, not so much with Gettleman. I had a hard time imagining Reese winning an argument with Coughlin, whereas with Gettleman I definitely had the sense that it was his vision that the Giants were following. But one thing the Giants have managed to do since the well documented Parcells/Young clashes is to keep a lid on any clashes there may have been between coach and GM, and there surely have been many, it's the nature of the business.
When Young was GM, he had unique powers that were guaranteed in his contract. Ownership did not have the power to overrule his personnel decisions (and that included the head coaching position). They could fire him, but they couldn't pull rank on him. No Giants GM since has been granted such final say nor will any likely in the future.
One of my favorite examples of Young's use of power was when the late, great Tom Boisture and the recently late, great Dan Reeves disagreed in 1995. Reeves wanted Rashan Salaam and Boisture wanted Tyrone Wheatley. What I found so interesting was that Young's preference was Korey Stringer, but rather than use their disagreement as an opportunity to grab his guy, he went with his head of college scouting; because managers manage, coaches coach, and scouts scout.
Too bad, too. Stringer was better than the both of them combined and maybe he would've avoided that tragedy on a different team in a different camp.