I don't think it's crazy to provide default behavior to keep the learning curve down. The default relationships already exist within socket [0] and timer [1] units. I think it's even more unexpected for someone to *have* to use X-Fleet options to make core systemd functionality work as expected.

And to be clear, this behavior should be more sophisticated, as a user can alter these relationships [0] [1].

[0] http://www.freedesktop.org/software/systemd/man/systemd.socket.html#Service=
[1] http://www.freedesktop.org/software/systemd/man/systemd.timer.html#Unit=