That's to prevent leaks from driving the stock price up, and causing the buyout cost to increase. That's a little different than using it to hide the fact that they were knowingly breaking the law. Do you understand the difference?
You're making the assumption that they did it for that reason. It could be that covering up the crimes was just a side effect.
Other than covering up crimes, what advantage do you imagine would be worth the loss of those benefits?
But there's also just cleaning out all the cruft which makes finding useful stuff harder. Since going all-in on Gmail, I delete far less than I used to and that's not entirely a bad thing but I also have to sift through a lot more stuff when I'm looking for something.
> Doesn't need to be something you did that was wrong
Deleting something that can be produced of evidence of wrong-doing is illegal all by itself.