Pretty much spot on, as you say, @Out is only required if the object reference may change and you want it updated in the relevant context after the action method has completed.

If you just mutate (e.g. use a setter) an injected component you don't need to outject it.

Raise a feature request against the documentation in JIRA if you think it could be enhanced. Chances are if you weren't sure about it then a bunch of other people aren't/weren't either!

You might outject to a different scope or different context variable, or both. Any examples of this I can think of would be pretty contrived, but I'm sure someone will think of one eventually.

You might want to outject something from a conversation scoped component (where you can use your SMPC to prevent LIEs) to the businessprocess scope. As for variable name - perhaps in a large app where you want shorter names in the class?