Document more thorougly use cases for a function

[bkalcho]

What problem are you facing?

It looks little ambiguous the usage of this function by the documentation description. Maybe, I have misinterpreted, but the XR/XRC by the Crossplane documentation interpretation is marked as ready by default when all of the composed resources from composition are ready. So when using the Composition in the pipeline mode, what is the use case of this function? What gap do you want to fill?

How could this Function help solve your problem?

As I had mostly experience with now the legacy Resources mode, maybe something changed in the newer Crossplane versions. Nevertheless, I haven't seen it clearly described in the documentation, neither in this repository nor in the Crossplane docs. Adding such a use case and description would be great to remove ambiguity. I understand that the function will mark the XR ready automatically when all composed resources are ready, but confused why I need it when this is default behavior.

[phisco]

Short answer: composed resources' readiness for a function pipeline is not the Ready condition being set to true by default, it's left to each function to implement its custom logic and report back whether a resource is ready or not. This function just does that, automatically reporting a composed resource as ready if its Ready condition is set to true.

But I agree it could be more explicit both in the crossplane docs and here.