A user profile is a collection of properties that describes a single user, along with the policies and other settings associated with each property. The user that a profile describes is represented by a unique identifier in the profile, and the remaining properties provide information about that user, such as the user's phone numbers, manager, office number, job title, and so forth. The set of user profiles for a SharePoint deployment are stored in the profiles database associated with a User Profile Service application.
User profiles help identify connections between users in an enterprise, such as their common managers, workgroups, group membership, and common Web sites. They can also contain critical information about a user, such as the products the user works on, the user's interests or areas of expertise, and the user's place in the organization's structure. By exposing this information in features such as My Sites, user profiles provide the basis for enterprise social networking in SharePoint Server. Some of the enterprise social networking features that user profiles support are:
- My Sites
- Profile pages
- People searching
- Organizational charts
- Expertise search
- Social tagging
User profiles are distinct from SharePoint Server user accounts and
exist in their own data store. User accounts provide security and
access rights to objects in SharePoint Server. User profiles are used
to organize information about users and about the relationships among
users. Updating a user's profile has no effect on that user's user
If you used the SharePoint foundation 2010( as in foundation their is no user profile service), you may noticed that no user information synced from AD.
You can have just user profile services without sync / mysite but in that case you will see user information once they will login in sharepoint sites. I would go atleast one step foward, configure the UPA and sync services but dont configure MySite...In that case you will get sync data from AD to SharePoint.