If it was about actual preparation then teams wouldn't be flying round the world for pre-season, it's just ridiculous.
I'm surprised more Managers don't complain about this, perhaps they do quietly but are then told to pull their heads in by their clubs.
Can't imagine the likes of Mourinho and Wenger are happy about the jaunts they're being sent on in pre-season these days. If they were given free licence on planning pre-season I doubt it would include many flights at all, and certainly not long ones.