This section from Ally Gold's piece:
Postecoglou has admitted himself that some might find his ways extreme, with his relentless attacking, possession-based football, with near non-stop training sessions of 60-70 minutes during the season to reflect the time the ball is in play during a match. In pre-season the work is even tougher to prepare the players' bodies physically for the energy required in the months ahead.
Particularly for our more attack-minded players, it's crucial for Ange to learn how quickly their footballing brains work when the focus is on quick, pass & move, attacking play.
Under Mourinho, Nuno & Conte, they've been drilled into safety-first, getting back into shape, safe rather than risky play. So pre-season is partly about changing the mentaltiy, and seeing who flourishes & who looks lost.
Then, next, Ange needs to see which players can physically survive the relentlessness, without their bodies screaming "no mas", or getting injured.
For instance, GLC may look creative & dangerous in Ange's attacking system. Whether he can physically survive pre-season is another matter altogether.
And there's risk too. Any of our "sellable" players who get injured in pre-season will likely still be with us come September.