Being able to define output fields that are returned from the webhook associated with a Custom Workflow Action could be very useful.
You can do that with Custom Code Actions, but that’s not as user-friendly an experience for non-developers (and less than ideal for bits of logic you want to reuse across many workflows).
You can also get close by using using the Server Response value of a generic webhook call in Simple Branch or Copy Value steps, but not in a way that can separate out multiple values, parse data types, etc.
For reusable steps that aren’t supported in Workflows, being able to have a clean, parameterized custom workflow action with return values that can be used downstream would be much faster and more flexible than the alternatives.
For example, people could add their own action step for “Previous Value of Property was X”, and use that for branching. The closest built-in option (“Value has ever been…”) is not sufficient for this case.
There are all sorts of similar workflow gaps that don’t seem like they’ll be addressed—but could be within the app ecosystem—using Custom Workflow Action output fields.