I am looking for an example in the real world where only a portion of the entire data set is encrypted even though the entire data set is considered sensitive. Specifically the portion that gives context to the rest.
For example (maybe a weak example). If you had sets of data on personnel, some of the raw data associated with each person may not be encrypted, because its easier to transfer if it isn't, but the identity of the person or any other critical context-providing data is encrypted.
The purpose of this would be to make manageable the transfer of the majority of the data across unsecured platforms easy. The encrypted context data could be carried separately and married back only when needed.
You are a doctor, and you want to use data from patients in a research project (Hospital research, not academic...). Part of the work is showing and comparing data with other doctors. This means you email ppt and excel spreadsheets with patient data. Most of the time the other doctors don't care about who the patient is (identity+more complete records) while they look at the data sets (maybe at the end, when they need to decide next steps). When they do, you want them to use their own access to get further patient records. But in order to do that, they need to have keys for each patient. These keys would be carried with the decrypted data.
You can't send and share the data encrypted. It doesn't work. one guy has a ipad, another has a windows netbook. And the engineer turned doctor has a linux distro running on an old mac laptop which he takes great pains to tell everyone works much faster than it did with OSX.
Excel is not secure. Even if you could deliver it encrypted, as soon as it is readable, it is copyable.