Cleverley adds a real balance and it's horses for courses.
For me, Mirallas is always just too predictable on the left in that he constantly looks to cut inside and shoot or dribble his way in-field.
He's better - as a winger - on the right, and when he does start on the left he always almost is only then really effective when he plays mostly as a second striker and Baines/Oviedo pushes up - like he did at Chelsea in order to latch onto Lukaku's flick-ons etc.
Cleverley offers solid workrate and reliability but also a real sharpness and speed to his play - always looking for a forward pass etc. It's typical of players who came through Utd's academy learning from the likes of Carrick and Scholes.
In the centre, for me, he isn't as effective as he tends to prefer to get forward and that exposes gaps around Barry and also negates space for Barkley - who is most effective when he has a link-up player (Cleverley, Lennon, Pienaar or even Osman) to combine with in tight areas. Stoke and Newcastle are perfect examples of that.
For me, if we are to start two wingers, then it has to be Lennon on the right to keep the balance and link up with Barkley, and then Kev on the left to basically drift inside and be the player to get in and around the box with Lukaku, allowing our left back to push on.