Still new and learning, but this is what it seems to be about, this question?

If you want to embed utility in the flow of making or reacting to casts, then:
Composer Action: Get people to use your tool when creating casts.
Cast Action: Get people to use your tool when reacting to a post.

Use Frames when you want a rich, interactive experience inside a cast (polls, forms, games).

Use Composer Actions when you want to be part of the post-creation experience.

Use Cast Actions when you want to add value to an existing post (quick links, reactions, payments, etc.).

Is my understanding correct?

Sorry, I was trying to comment on @dwr.eth 's post. I guess I clicked cast instead of reply lol. Again...a few day newfarbie