Usually at some point the server needs to be able decrypt the data so it can be displayed to a user, so the key needs to be handy. So if you have the key and data on the same sever it's of little security value.
If you want to have this data in some kind of database, there is a good chance you want to be able to search and index this data. Possible to index and pre-sort encrypted data without giving away the content?
Yes, maybe encrypt some sensitive parts, but encrypting all customer data is counter productive.
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