Overhead of Using APFS Encryption
T2 Intel and Apple silicon Macs invariably encrypt the Data volume on their internal SSD; adding the protection of FileVault’s password comes at no cost.
Some external SSDs can use APFS encryption without any reduction in performance at all.
Other external SSDs may show reduced write speed to APFS encrypted volumes, particularly when they are connected via a hub rather than directly.
Currently the only way to tell SSDs apart is to measure their write speeds.
This third point is not what I would have expected.
