Comment 6 for bug 1847389

If the pool has an _active_ (and not "read-only compatible") feature that GRUB does not understand, then GRUB will (correctly) refuse to load the pool. Accordingly, you will be unable to boot.

Some features go active immediately, and others need you to enable some filesystem-level feature or take some other action to go from enabled to active. The features that are left disabled in the upstream Root-on-ZFS HOWTO (that I manage) are disabled because GRUB does not support them. At best, you never use them and it's fine. At worst, you make one active and then you can't boot. Since you can't use them without breaking booting, there is no point in having them enabled.