This is the way to change over a squad.
One of the big mistakes under Moyes and LVG was that we were selling players before we had any replacements. As a result we would end up with just our youth team players at critical points in the season.
Mourinho kept his squad together and just added quality in four players. He ended up freezing out Schweinsteiger, but other than that it has been pretty smooth.
As it has turned out, Rojo and Jones have proved useful, while Schneiderlin and Memphis have moved on. But if you were doing a clear out last summer, then it might have been the other way around.
Mourinho can now focus on strengthening with a few good players in the summer with the space already there in the squad. And the squad can improve without too much change all at once disrupting the process.