It's also early days to tell if it'll work for Juve or any other club who does this, isn't it? With Gallagher, Chelsea already had others to take over from him.
Who knows, it could be a worse trade if Juventus back up their words with actions and let a player to rot in the reserves for half a year - then fewer clubs will want the player, the player will be worse.
All in all, the total value could go down a lot. If you then take the player back up from the reserves, you'll then show the other players that your threat was just an empty threat.
I'm just not completely sold on threatening a player with no football, if you got nothing better available already.
Edit: Imagine we did this with Casemiro. So much money just sitting in the reserves, and he'd probably would want to just cash in like that instead of going to Saudi Arabia and getting a similar wage.