Both can be used for reusability.
- A plugin recipe is a python code that you have packaged as a visual recipe: with inputs, outputs, and parameters.
- An application-as-recipe is a sub flow that you have packaged as a visual recipe. So it can be a sequence of several visual or code recipes executing to generate an output.
Python or R recipes can be converted to custom recipes
You can check this link:
For the app-as-recipe you can check this: