When to use setup() vs. map helpers?

[plweil]

This is kind of a followup to #1261 , but is much broader. When should we use the map helpers and when should we use setup() to import stores into Vue components? Is there a rule of thumb for this regarding a) your project is in Vue 2 versus Vue 3; and b) your project is using the Options API versus the Composition API? Or can you mix and match? One partially-developed project just given to me uses Vue 3, the Options API, but pulls in Pinia stores with <script setup>. Is this ok, or is it a problem?