The key benefit is that a single process has a harder time monopolizing the system and taking over the system as a whole. This allows you to write code where the code is known to be suboptimal because it cannot take over the machine. In contrast, many other systems relies on a proactive model where each line of code has to be scrutinized for utmost correctness, or your system as a whole will fall.

As for the faults, there is a subtle but important difference compared to exceptions: you handle any error, not just the ones you figured could happen. And because resources are bound to processes, when the process goes away, so does its resource. Usually you would have to handle this in other languages.

The final point is that a fault is made transient: the system recovers and reestablishes the last known good state/invariant of the system. This allows you to try again which often handles the fault. And if it keeps failing, the fault is escalated to gradually larger and larger parts of the program.

There is nothing magical about the model. It is just that other languages have next to no convenient support for it.

Not always, because that thread might have written to so some shared data structure and left it in an inconsistent state. Restarting that one thread might seem to work but because there is no guarantee, the safest way is to restart the OS process.

It might not even be your code. Maybe your RPC library or some other package did it internally. You might restart and 99% of time it will work, but it will not be a guaranteed thing.

Now, of course the equivalent counterpart to this is not threads but you can do this with OS processes. And I've done it in Python. You can use pipes, file system writes, sockets to create a reliable system were some processes can crash without bringing down the whole service. But it is cumbersome.

But imagine the sever handles a million connections. Certainly doable in Erlang. Each one handled by one lightweight process. Connection does something unusual, maybe uses a new feature which was added last night. It crashes, that's fine. Other 999999 are ok. If this was a C++ program, it might have segfault-ed and caused the other 999999 connections to be dropped.

I've seen systems which had a periodically crashing subsystem that was being restarted behind the scenes for a while most of the system stayed up without noticeable issues. In business terms that means a smaller ops team, it means not having to wake up at 4am to answer pages (if subsystem heals itself, can just fix it in the morning) and so on.

Moreover, live code hot-patching is often touted as a gimmick. But I've used on a large production clusters while it was serving tens of thousands of requests per second without stopping. Sure it was scary and by that time something has already gone wrong (to need that fix), and it was nice not having to to shut down everything just to add an extra trace or log statement.

Scala's Akka library is another place you can find this (although a bit harder to configure) but I don't know many other languages that offer this.