Loading McDavid and MacKinnon on the same line makes zero sense.
1) They are the top 2 centers on the team and should be used as such.
2) They are both player drivers and puck carriers
3) Having all that explosive speed on one line is not as good as having it on the ice for 40 mins of the game.
4) Crosby and MacKinnon already have loads of chemistry from years and years of training together.
Load up ocassionally throughout the game maybe, but regular shifts they should he apart which is why they are.