Turret plating is a monumental failure. Games are decided earlier, but forced to play out longer.
What!? Adding more early game income makes games snowball out of control faster!? Who could have possibly seen this coming?
The team with the early advantage cashes out on turret plating, and then once plating drops, they cash out a second time on the actual turrets. All while giving the illusion that your team isn't losing, because hey, your turrets are still up and it isn't obvious that the enemy team is up thousands of gold when you check the scoreboard!
Unless the game is even until plating falls off (which virtually never happens), the winning team is just getting double gold in the long term and a more consistent power incline prior to the first turret falling, making it much easier to maintain and snowball off of any advantage.
This is probably one of, if not the, worst changes made to League.