There are many good comments here and from what I've read immutable seems best suited to the Enterprise IT environment where you don't want the user fiddling with the system, and you want built in rollback and quick configuration. As well as user data protection.
But for Linux users at home I don't see any massive advantage. Especially if you're running a reliable distro like Mint or Debian, or better yet Linux Mint Debian Edition is the best of both worlds.
If you only turn the PC on to watch YouTube, read a document, scan and print, surf the web or game your system should be 100% ok. Unless you're running Manjaro or Arch.
What I don't like about the immutable approach is that it turns my PC into a dumb terminal locked by the distro Devs and updated at their will. It's ok if I have read only on my Android phone because I don't need to get into root etc. That's a good place for immutable.
But I don't want my Linux box at home to be a just an appliance that someone else essentially has control over.
That's very much an Apple approach. Don't let the user see or touch anything. They can just be content to change the wallpaper and add a widget. We'll decide when and how the OS gets updated, what apps they can and cannot run etc.
Ultimately it infringes on user freedom and the very FOSS principles that set Linux apart from the rest.
In short, fine for Enterprise IT but no good for the average Linux user.