In a Google account (sync), what is the difference between Contacts and People details?

For a Google account, you are allowed to sync Contacts and People details. What is the difference between these two?

Answer

The best explanation I could find online:

People Details is a new sync service related to the recent release of Google Play Games. It was pushed to most (if not all) android devices recently. Its purpose is to tie you together across all Google Play services (the separate services available from the Google Play screen). The idea is to maintain a uniform and unique "identity" for you in all related Google Games so that data from one can potentially be used to "enhance" the user experience in another

The contact sync is for the usual contacts that a user saves directly on your phone.