The common notion appears to be that by bringing in a manager who suits your current playing style/tactical preferences, it provides greater scope for continuity and ultimately, success. I remember thinking that Pep would have been a great transition and extension on what Van Gaal was attempting to produce at us. Just taking the link posted by
@jasT1981 at face value, though with a huge pinch of salt, question becomes how similar are ten Hag and Ancelotti stylistically and who would be similar to Ancelotti if you were thinking of a long term successor for him?