Eliminates a malicious threat vector. Gives you piece of mind to charge your devices without worry that what you connect to is going to interact with your device.
You finally described a reason for these otherwise frustrating cables to exist! Though I like the other suggested method better, a charge-only adapter that you apply to the end of a full featured cable.
it's also safer when wanting to charge from untrusted chargers, though you can still get an adapter to block the data pins or just bring your own wall charger/battery when traveling
I think power only cables should exist because they are significantly cheaper, but they should have some kind of marking to differentiate them enforced by the standard