Services which may be enabled by Default
If a service does not require configuration to be functional and does not listen on a network socket, it may be enabled by default (but is not required to do so).
In addition, any service which does not remain persistent on the system (aka, it "runs once then goes away"), does not listen to incoming connections during initialization, and does not require configuration to be functional may be enabled by default (but is not required to do so). An example of "runs once then goes away" service is iptables.
Finally, there are some services which are permitted to be enabled by default as specific exceptions. The list is shipped as part of the systemd rpm: 90-default.preset.
All other services must not be enabled by default. If you think that your package contains a service that should be enabled by default, but does not meet the above criteria, you may request an exception from the FESCo and later file a bug against the systemd package.