At least from what I've read, he's more comfortable at center. Varies from player to player.
I've felt that Couts would be better at LW, b/c as he ages and the league gets faster, his lack of speed is exposed.
At wing, he doesn't have to get all the way back to his own net and can be more aggressive on offense.
Cates was a top defensive center as a rookie, when he came back from injury he was a solid LW, last year when back at center with Brink and Foerster, played at a 2C rate. Still learning to integrate his defensive responsibilities with more aggression on offense, but he's a true center now.
Nesbitt went high b/c he was seen as a true center. Depends on the defensive scheme, but under Torts and probably Tochett, centers are like a 3rd D-man in a 3-2 zone, which is a tough role for an undersized center to fill.
That's probably why they had lukewarm interest in Rossi and had they signed Shabanov, probably would have moved him to LW. And that's the issue that Zegras has to address along with FOs, can he be adequate as a defensive center (no one is expecting a Selke candidate, just don't suck).