> What is the benefit to the average user of running their own server?
All the server-side use cases you can't do with a client alone. I think you misunderstood my comment; I'm not saying that running your own email server is easy, nor that it's hard but still worth it; I'm saying that the fact that it's too hard to be worth doing is a statement about the software that exists today, not some sort of immutable feature of the universe.
Anyway, that's the wrong question. The right one is: what new software would we make if everyone had their own server? The answer is, I dunno, but the hardware is good enough to find out; a cheap virtual server costs about as much as a streaming service, and quite a bit less than a mobile plan. It's well within reach for everyone in America to have their own VPS running their own email server. They don't, because Gmail is way easier, but that would cease to be true if we had better software. And, once there were a few server-side apps that were actually good, we'd probably make more (just as the advent of smartphones led to a lot of new use cases that would've been difficult to imagine before they were commonplace).
> not some sort of immutable feature of the universe
Except it is. Running your own server will always be more work than letting someone else do it, so unless there is a strong incentive people will let someone else run their server.
This is basically the Law of Leaky Abstractions. At some point you will have to deal with a problem yourself because no abstraction is perfect.
Why is there a graphical installer for the Minecraft client and not for the Minecraft server? Because of some fancy Law with Capital Letters, or because more work went in to the former than the latter?
All the server-side use cases you can't do with a client alone. I think you misunderstood my comment; I'm not saying that running your own email server is easy, nor that it's hard but still worth it; I'm saying that the fact that it's too hard to be worth doing is a statement about the software that exists today, not some sort of immutable feature of the universe.
Anyway, that's the wrong question. The right one is: what new software would we make if everyone had their own server? The answer is, I dunno, but the hardware is good enough to find out; a cheap virtual server costs about as much as a streaming service, and quite a bit less than a mobile plan. It's well within reach for everyone in America to have their own VPS running their own email server. They don't, because Gmail is way easier, but that would cease to be true if we had better software. And, once there were a few server-side apps that were actually good, we'd probably make more (just as the advent of smartphones led to a lot of new use cases that would've been difficult to imagine before they were commonplace).