1) Security has to be enforced by code
2) Your employees are reasonable, and won't try to maliciously bypass security controls
I'm firmly in camp #2. In a normal corporate setting, a locked door or a locked cabinet is security, even with a cheap, easily pickable lock.
That's all this is. And for 95% of corporate applications, that's good enough. If you have high-level executive crime, or a scandal where you killed a few people, this won't help, of course. But if you'd like to keep an upcoming merger confidential, or maintain a trade secret, or anything vaguely normal, this is more than good enough.
This also helps with email retention policies. Sometimes you want ephemeral communications you don't want a record of. This isn't necessarily malicious either; in more litigious industries, emails can be obtained through discovery and quoted out-of-context. Things like typos can get you (goodness knows I've made enough of those). Sending an email which communicates something and disappears in a week is helpful.