About Encryption of SYSTEM, SYSAUX, UNDO and TEMP tablespaces in CDB/Root Container

Oracle 19c v12

Hi,

What is the reason of Oracle's recommendation (see below) about encrypting default tablespaces within CDB's?

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Using Transparent Data Encryption with Other Oracle Features - Section 8.2.3, Step 12

"12 -Perform the following steps in the root container.

1. Optionally, encrypt the USERS tablespace in the root container. While technically possible, you should not encrypt the SYSTEM, SYSAUX, TEMP, and UNDO tablespaces of the root container."

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And is that recommendation only for applications using Oracle Key Vault and Data Guard?

Would that be the same recommendation for applications using HSM wallet or applications not using Data Guard?

Thanks