That's fine. But when Malcom was signed for example, EV didn't rate him or needed him. Situations like that are not good for anybody, nor the club, the player, or the manager.
Abidal was a stubborn SD who weren't convinced with the coach and was trying to prove he is the "alpha" in a desperate way, denied EV request for LB which was essential, didn't try to bring a proper tactical replacement for Paulinho and forced the player he wanted on the coach (Vidal, Malcom, and maybe Griezmann) who were awful fit.
Such situation should be avoided.
Same happened with Koeman being stubborn with the signings he didn't get, like Pjanic. A situation that should also be avoided as Xavi has to respect the SD and his signings and be fair to all players.
Another awful situation to avoid was having coach who has all the say in the signings, like we did in summer 2015 and ended up with the Spanish Vidal and Arda.
And the last of awful situations we had is the board interfering with SD job, like Rossel board doing with Zubi.
A balance is needed, Xavi will never find the next Pedri or Araujo by himself, he and the SD should be cooperating together without board interference, last time this happened was in summer 2014, and before that it was under Txiki.
New SD being hired after coach is risky though, and one of the reasons I am disappointed with Planas departure, it is bad timing.