The performance is a good point. You can do the striped mirror with ZFS too and still get the advantages of ZFS.
I think you can do all of that through the Proxmox UI, but it shouldn’t be too hard to do on the CLI either. You just make two mirror sets and you’re good to go. ZFS should automatically distribute the load across the two mirrors.
Few of them for most use cases, especially a VPS. My server have a couple of IPs each mapping to a different VM, they can all claim 22/80/443 as you’d expect, but that’s just basically the same as having a bunch of VPSes anyway.
It’s useful for some other uses like, I might want to dedicate an IP for VPN exit that doesn’t expose any services.
Another use is sometimes you just want two things to stay entirely separate, even if on a technical level it could work with a reverse proxy. It can eliminate some class of exploits like request smuggling.
One use case I’ve had for a customer is they have a system that can only do TLSv1.0, which is wildly obsolete and exploitable. So that particular API endpoint was served from a secondary IP, that way I can continue to enforce TLSv1.2+ on the primary IP. It’s possible with some reverse proxy magic with HAproxy, but I could also just make a new server block in the existing NGINX bound to that IP and call it a day.