It's a pretty stupid tactic, because judges can give instructions to juries to presume adverse interference—assume that the emails existed at one time, but are

It's a pretty stupid tactic, because judges can give instructions to juries to presume adverse interference—assume that the emails existed at one time, but are not available in the present precisely because of these "CYA" policies—as happened in Apple v. Samsung. There's an offshoot of the Gell–Mann amnesia effect in play here. When programmers encounter Web sites that enact ridiculous requirements about passwords, they complain of bozos being in charge of technical decisionmaking, and then making decisions that either don't make sense or are downright bad based on nothing other than cargo cult advice. There are plenty of cargo cultists in management and legal departments, too, but they're often given the benefit of the doubt. Obviously they know what they're doing and have good reasons for everything, right? You know, just like the reason that a site requires you to have digits and punctuation in your password, but forbids you to have a 6-word passphrase because it's too long and contains spaces.