I think it was interesting that, when he came on, Lindelof moved to the LCB position and Maguire assumed (what basically is) Varane's position in the defence.
Given that we still use the left side a lot to advance the ball (40%), and that when Rashford plays there we often look for the early ball in-behind, this may have its significance.
It can potentially be a smart move from ETH. Maguire can revitalise his career in a more natural defending role and without the burden of having most of the build-up going through him. Still a very expensive mistake (we forked out the big money expecting him to do what Martinez does. And the latter didn't come cheap, either), but with Varane out, maybe we've found a role for Maguire.