Locks and keys are usually more an inconvenience to prevent casual abuse of your boundaries. People who want access, nefarious or otherwise, will gain access, whether it's cops, ninja assassins, or junkies looking to strip your house of copper.

Ninja assassins are low on the list of possible threats, but never zero.

The biggest risk to me personally is the junkies and porch pirates, so signs and out of reach and very visible cameras have gone up to make them uncomfortable and feel too paranoid to mess with the locks.