Regarding "there is little magic", Poettering repeatedly praises socket activation in his blog. It's not a new idea, but an old one that fell out of favor because it kinda sucked (remember xinetd?). It's about pretending that a service is running when by providing its listening socket, then starting it when the first client connects.

It has some problems: it's more complicated, it can actually slow things down compared to starting a service as soon as possible, and it has new error cases because of course "pretending that a service is running" doesn't have exactly the same effect as actually having the service running.