The more information you can collect about your users, the more personalized you can make your messages. Preferences centers are a great place to allow users to tell you more about their preferences and who they are.
Update Customer Fields
To add a custom field linked to a customer to a preference center you can drag in a new Text Box element and link it directly to a field on the customer.
You typically don't want to make these extra fields required because someone should be able to update their subscription preferences without supplying new information.