One of the features of all modern Macs, whether they have Intel processors with a T2 chip, or are Apple silicon models, is that they all encrypt the Data volume on their internal storage. So why should you enable FileVault when the volume is already encrypted? This article explains the difference, and why every Mac running recent macOS should have FileVault enabled on its startup Data volume.
Intel Macs without a T2 chip
The situation is clearest in Intel Macs without a T2 chip, as by default they don’t encrypt any volume. As they can be booted from an external disk, anyone who gets hold of that Mac, even for a few minutes, can steal what they want from it. Although encryption does impose a small overhead, all recent Intel processors have instructions that accelerate it. You’re unlikely to notice the difference in performance, although initial encryption can take many hours for larger volumes. If you’re planning for a clean install of macOS, that doesn’t matter, as you can enable FileVault before you migrate anything to it, when encryption is quickest.
Read more at eclecticlight.co