Comment by gsnedders

Note there's also macOS-related reasons to use the different modes:

Reduced security mode is needed to boot into outdated macOS installs (specifically, I believe this is "outdated, insecure, at install-time"), along with loading kernel extensions (which aren't supported in full security mode on Apple Silicon).

Permissive security mode is needed to boot into macOS with a custom XNU kernel.

But yes, this is a significant change to iOS devices, but not to older macOS devices.