When you want your gate key to be the same as your gas and trunk key.
The only issue with this "lock" is that it's less of a security mechanism and more of a test of strength between you and the person coming in. If a 300-pound linebacker gives the door just one good yank, he'll probably send you flying from the toilet seat with who-knows-what strewn all over the floor.
It's possible this kludge was only made to keep the trunk from flapping. Sure. That's it. Because if it were meant to keep someone from opening it, it would only work for someone on the inside right? And that would mean... never mind, I don't want to think about it.