It's really easy to use.
Our patients already have a couple ways to securely share data with us. First, they can write the information on a piece of paper with their option of a pen or a pencil (we're that flexible) and bring it in to their provider. Second, they can manually enter the information into our online patient portal, Duke MyChart (when enabled by their provider).
HealthKit will eventually provide a third option, but rather than having to remember to write the values down and bring in the piece of paper, or having to remember to manually enter data in to a website, HealthKit will automate this process.
For example, if patients choose to share their blood pressure with their provider using HealthKit, and this feature is enabled by their provider, they need only give permission to the appropriate app, after which their data is securely saved to their electronic medical record. Any subsequent blood pressure measurements can be saved directly to the medical record in the same way without any intervention by the patient.
It sets a clear expectation that users are in control of their data.
Unlike personal health records that have come before, Apple has approached this problem differently, and has decided to be a data broker rather than a consumer of the health data. This is a big deal. At every step along the way, users are informed that they have control of this data. No data is shared without their express permission, and at any point in the future the user can easily revoke any app's access to the data. The data itself is only stored locally in the device's secure HealthKit data store.
While cloud services and Big Data promise to revolutionize data sharing, HealthKit will have none of it. In fact, Apple recently updated their App Review Guidelines to expressly forbid that any data obtained from HealthKit be stored in iCloud: