I’m not using an immutable distro, but I am daily driving a KVM-based Gentoo setup where most of my VMs use transient (immutable) storage and iSCSI where persistence is required.

I’d say that immutability has a ton of benefits for security and reliability, but it’s important to be able to customize things when needed. I’m not sure an immutable distro would offer much in the way of customization though.

In my case I am generally unable to harm my system without meaning to, and I’m able to test new configurations without issue. I have lost data before when accidentally saving to a transient disk, but this is something I could fix with better scripting.

I’d say that in general, incremental backups are a better solution if you’re only looking to avoid messing up the system. But immutability is a good option if you like containers or have some other way to configure things before locking them down.