The main benefit is that the base system is immutable, which should make it much more reliable. So to get new software, instead of doing a zypper install ..., you'd leave the base system alone and only install packaged apps (e.g. flatpaks). That way you don't get conflicts between package versions and upgrades can be predictable.
I don't have direct experience with it, so I don't know how well that works in practice. But I definitely like the idea of using it for my NAS, which doesn't need a lot of updates. It currently runs Leap, but MicroOS should be a relatively straight-forward switch.