Lets say one has a debian server with 256 cores and 100 users. If an user wants to run fedora it makes it possible. Not just build and run once but keep running for 365days and in that fedora give 200 user accounts or 200 webservers. It is possible with lxd. I know some hosting companies use it. Mix and match. All these run as non root. You can do ram/cpu/bandwidth/io controls everywhere.
I already run all my containers as "non-root", I can run 200 Fedora images and I can do ram/CPU/bandwidth.
I can also put that users home on the SAN so their data is retained if the container has to move servers. I'm unclear what that has to do with being an LXD advantage.