Linux

The most basic benefit of immutable OSes like Fedora Silverblue is that you are prevented from messing up your system enough that you are unable to boot into it and fix it. This isn't strictly true, you can always go out of your way to screw things up (say deleting required partitions), but in normal usage you will always have a backup to boot and fix whatever you messed up. It also makes it extremely easy to undo things even if they aren't errors.

It's possible to do this without immutable OSes using btrfs snapshots before you change anything system-wide, in fact I believe MicroOS uses btrfs snapshots for their immutable system, but that adds cognitive load as it requires you to remember to create a snapshot. OpenSUSE Tumbleweed provides snapshotting automatically and adds entries to the bootloader for previous iterations, but it isn't immutable because you can still go and modify your root partition without taking a snapshot. MicroOS, however, has a read-only root partition so it becomes a lot more difficult to make a change without a snapshot. You can still do it, but you have to go out of your way to do it.