[tannerc]

Doctors, for checking activity/sleep/etc.

Friends/relationships, for checking general activity and check-ins.

Potential businesses, for seeing interests and the like. Or, if currently employed, the employer could randomly check to see how the employee has been sleeping (are they going to be tired/cranky today?) or to see how often they check-in at the office.

Aggregated with more data from people doing similar things and you can start to get a look at populations (what if everyone in SF was logging this data? What if a good chunk of those in the US were?).