I'm not sure how systemd does it, but in my vision, there should be
two different states for the service: the *wanted* state, and the
*current* state.

The wanted state is what is set by the administrator when she runs
a command such as "rc thisrunlevel". The command should set all the
services in "thisrunlevel" in the "wanted up" state.
The current state is exactly what it says: is the service actually
alive or not, ready or not?

A service manager's job is to perform service state transitions
until the current state matches the wanted state - or an unrecoverable
error happens, in which case the admin should have easy access to the
current state in order to diagnose and fix the problems.

--
Laurent