Which feature is NOT part of the Smartsheet functionality for managing users?

Creating custom fields is not a feature specifically designed for managing users in Smartsheet. Instead, custom fields allow users to enhance their sheets with additional information relevant to their projects or processes. This function is related to the configuration of data within sheets, rather than the management of user accounts or permissions.

On the other hand, assigning roles, managing user licenses, and tracking user activity are all integral aspects of user management within the Smartsheet platform. Assigning roles allows administrators to define what permissions and access each user has. Managing user licenses is essential for keeping track of how many users can actively use the platform based on the organization's licensing agreement. Tracking user activity ensures that administrators can monitor how users interact with the systems, which can be valuable for security and compliance purposes. Thus, the distinction between user management functions and features designed for sheet data management is what makes creating custom fields the correct choice in this context.