Honestly, IMO the end-user benefit is mostly that it sounds cool.

All the benefits I've heard (including the ones in this discussion) don't actually derive from "immutability" but from releases that stay the same for longer (which is what "more stable" used to mean), or the ability to roll back your system to some "known" working state (which you can do with snapshots and in a plethora of other ways).

What immutability means is that users are unable to alter their system, or at least not expected to... basically, it means what in corporate lingo would sound "altering your system is not supported" and that the distro actively makes it hard for you to do so.

This means users will not break their system because they followed badly some instructions they found on some badly written forum post anymore and blame the distro for it, but it also means that users who actually have a reason to alter their system and know what they are doing will have a hard time doing it (or be unable to), which is precisely why I left macos and went back to linux for my work computer some ten years ago (I spent half a day doing something I could have be done with in five minutes and said to myself "never again").

For the team/company that builds it, an immutable distro will likely be easier to test and maintain than a "regular" one, which should then indirectly benefit the users (well... as long as the team/company interests are aligned with the users' of course: shall windows get easier for microsoft to maintain, how much benefit would trickle down to its end users?).

Users who switch to an immutable distro should see a decrease in bugs short-term. In the longer run, I'd expect distros (especially the "commercial" ones) to reduce the effort they spend in QA until quality drops again to whatever level is deemed appropriate (if bread costs less I'm still not gonna buy more bread than I need... same goes for quality).

Basically, it all boils down to "immutable distros cost less to maintain" (which, don't get me wrong, is a net positive).

I must say I find it slightly concerning to have heard several "veteran" linux users say that immutable distros are so great that they will install one on their parent/child/SO/friend's PC but on their own.

It's also a bit unnerving to notice that most of the push for immutability seems to come from companies (the likes of debian/arch/gentoo/etc. are not pushing for immutability AFAIK, and they certainly don't have the initiative in this field).

I'm not sure how much immutable distros will benefit the community at large, and... I'm not even sure they will end up being very successful (windows/macos follow in whatever makes is more profitable for microsoft/apple, linux users have choice).

I hope that immutable distros will prove both successful and good for the user community at large.

edit: Forgot to explain the positives I hope for: since immutable distros should require less effort, I hope this will lead to more/better "niche" distros from small teams, and to distros with bigger teams doing more cool stuff with the extra manpower