Even when he's fit sir Alex seems to not trust him for some reason because he has been dropped many times over the years, instead of persisting with them to find form like he has with Ronaldo or Rooney, he drops nani on the bench. Nani for me is one of those players who should be a starter almost every game, as long as he's fit. On form he's our best winger, yet certain times he gets dropped for big games simply to be more defensive.
Like other people were saying, a switch to 4-2-3-1 makes the two wingers have much less defensive responsability and pushes them further up the field, at least that's how it's supposed to be. Sir Alex isn't the best manager at utilizing this formation to be honest, because he tries to keep the winger play deeper like in a 4-4-2 and provide defensive cover, and he wants the fullbacks to play the same. That is why we often look so out of ideas and defensive when we use that formation. We resort to doing long balls to Rooney and our wingers are too deep to help out, and our attacking midfielder (usually giggs) is way out of position because they don't actually know how to play that position properly. Kagawa will help that a lot, and it should help players like nani as well.
Also, I agree with people saying we need a team tha we know is our strongest 11, or at least most of it. The way SAF sees it, currently people who will always start are: de gea, rio, vidic, evra, carrick, Rooney
Even Valencia when he gets off form he gets dropped, as does nani. Our wingers you never know which two will play, and we have no idea who will be rooneys striker partner, or carricks midfield partner for this season. Same with right back, sir Alex seems to have nobody in mind when he thinks of who his best right back is, one moment Rafael gets a few games and then after one poor performance he is dropped for jones, or Smalling. I really think we need at least 8 out of the 11 positions nailed down with starters, and rotate the other 3.