Here's a fun feature of +systemd
's networkd, +Tom Gundersen
recently added: exit-on-idle. It will now exit whenever there's nothing to do (with a bit of latency). Due to the magic of socket activation (with a netlink socket) it is automatically started again when something happens, and there's a network interface coming, going or changing state. Behaviour of networkd is hence fully transparent, it will not lose any events on the system, even if it is not running! How awesome is that!?
Of course, compare that with NetworkManager's much touted new "configure-and-quit" mode: that too makes sure that the network management daemon doesn't run all the time. However, that's a mode to explicitly enable, and if you enable it you basically break dynamic network configuration for the system after startup completed, until system shutdown. It's kind of a "configure-once-then-break" mode... networkd otoh exits-on-idle by default now, and everything continues to work transparently even then!