[Montellese]

I never thought about this use case. The logic would probably be something like this: if a media import exists which imports all libraries of the respective media type and a new library is added it should also be synchronized. And something similar if a synchronized library is removed?

Being able to add one library initially is quite useful for testing and also for first setup. It means that one is able to use the device fairly quickly and then add all other libraries when viewing is finished. Especially for large libraries.
I just realized that if i choose All , then I can only remove All (ie after selecting All, sync and then selecting Choose.., no library is highlighted. That is fine for me. Can't speak for others). No auto sync here either.
As a workaround, after selecting Choose.., I can select the libraries that I want to keep and re synchronize.

Well as most of the user interface stuff this is still up for improvement. As I mentioned before I need to find a way to detect if some setting(s) affecting synchronization has changed to be able to force a resynchronization.