Custom Fields are perfect for tracking additional information you need to store on Stakeholders. They are meant to help you understand your stakeholders and status of relationship with them better. (Note that if you want to do extensive reporting on any of the fields, you would be better off creating them as Contact Groups as they are used more extensively as a filter in Reports).
Some examples of the types of Custom Fields our clients create for Stakeholders are:
Status of relationship with stakeholder (sometimes this is tracked as Initial Relationship and Current Relationship, to show a progression in how the relationship develops)
Demographics - age, language needs, etc.
Strategic objective for engaging with the stakeholder
Stakeholder mapping - level of interest, influence, impact
You can have as many Custom Fields as you like, but do remember:
Custom Fields are displayed in alphabetical order.
Use clear language to describe the field and the answer options
Try and keep the answer options unique (rather than yes/no responses for all) - this will make searching for stakeholders using Custom Fields as a filter easier as you search by the answer
You can 'hide' a Custom Field you no longer want by making it Inactive (in the admin menu)
You can import responses to Custom Fields using the Stakeholder Import Template