Other than McGoldrick our forwards and midfield players are much of a muchness so makes a great deal of sense to keep the legs fresh in there. I wrote a blog a couple of seasons back about how rotation is vitally important in the Championship (http://joefairs.blogspot.co.uk/2012/03/to-rotate-or-not-to-rotate.html).
I think Mick learnt this lesson the hard way on New Years Day when a leggy looking ITFC side was turned over by Brighton - since then he has often made sweeping changes to a second game in 3 days, or when there has been a midweek match.
It's not just performances on the night which improve but the break it allows players helps them stay injury free in a busy period over Christmas - but it was really noticeable that we looked very fresh in 2nd half as we closed the ball down high up the pitch with the likes of Hyam excellent at this.
We really do have a top manager at this level, which is no great revelation I know.