The idea is that a user could opt-in/out for (email) notification based on idea custom fields.
For example, when submitting an idea, we have one of the following categories to be assigned any idea: "Medical", "Logistics", "Finance", "Human Resources"...
We would like then users to subscribe for notifications within categories by their choice (ex: Medical and Logistics).
Thus the person will receive notifications only for ideas in Medical and Logistics categories (independently to the campaigns), and not Finance and Human Resources.
This selection could be done in the User profile.