I see several example launch files which implement a main, instead of just returning a launch description. Example from ros2/launch/ros repo: https://github.com/ros2/launch_ros/blob/master/launch_ros/examples/lifecycle_pub_sub_launch.py

Is there a guideline which variant to prefer? Are there any advantages in using the ros2 launch variant?

edit: This seems to be a conceptual question. From what i can see, the deciding part that makes the nodes run is the following:

ls = launch.LaunchService(argv=argv)
ls.include_launch_description(ld)
return ls.run()

It should be easy to include other LaunchDescriptions from other launch files like so:

client_launch = IncludeLaunchDescription(
        PythonLaunchDescriptionSource([share_dir, '/launch/client.launch.py']), 
        launch_arguments={}.items()
)

I dont see an advantage in letting the ros2 launch system take over the LaunchService, when you lose quite some functionality by not defining your own main.

For example:

• printing the introspection of the launch file
• performing tasks after starting the nodes, like calling services

What am I missing that the creators of ros2 launch thought of?