You're right in that it's a useful tool for various kinds of abuse, but so is almost every useful home automation/home security sensor.

The most obvious/useful use cases I can see are:

• turn on bedroom lights when the last person gets out of the bed
• turn off whole house lights when the last person gets into bed.

Both should be easy with load cells under the bed legs but rather difficult otherwise.

(Useful assuming a household of two adults in one bed that is).