When you have a tablet, you can do things like punch in what defense the other team just used to provide statistical analysis of what the next best play is, or what kind of defense to run if your opponent is doing X often. These are things a coach can know, or have on paper, but the ability to quickly look things up for an effective response or plan is probably very beneficial.
What I just heard is "coaches shouldn't be allowed tablets". Or binders.
Seriously, it's game/sport. Chess grandmasters aren't allowed to consult Watson in between moves. The players play the games. The role of coach mid-game should be more or less limited to deciding when to swap players, and arguing with referees over decisions. Coaching should be happening in between games. During the games it's time for playing.
But that's just my opinion.