Legend also uses the default prefix when adding a new item with the new-item dialog or at the top of an Outline. Basically any place where there isn’t something else that would influence which prefix to use. I agree with this implementation of a “default”. It doesn’t actually come up all that often, though, as you point out.
The auto-indenting after a Project that already has a child is intended and desirable; if Legend did not auto-indent that new child, it would end up becoming the parent and the Project would be left as a non-parent item above it. That probably isn’t what most users want.
Legend used to auto-indent an item created after a Project or Heading by pressing enter, even if the Project had no children. According to user feedback, Jay changed that behavior to the current one – seems like more people preferred that. That is a perfect example of never being able to choose a behavior that makes “everybody” happy. Jay generally pushes back on creating user-configurable behaviors in cases like this – better to just pick one and stick with it. He’s got a good point – it’s probably easier to write and test the app, and it’s easier for us to help each other on the forum when we don’t have to ask you what all your settings are before responding.
Half the time I wish new items were auto-children and the other half I don’t, so it doesn’t really matter to me which behavior it is : )