> Can you name a specific use case where you expect this to be beneficial?

An use case based on some feedback I received is:
Stage 1) Sync NAME,TEL,EMAIL 
      - First time DB population it will quickly create a browseable DB
        the fields chosen are the most important required for the 
        system usage.
Stage 2,3,4,...) Sync (Other Important Fields)
      - The DB is populated with extra (less important) fields 
        that may be required by the end user but it is nice to have now.
Stage last) Sync PHOTO or other fields left behind
      - The last stage is left for the most expensive but still required task.
The feedback I received are related to the deep knowledge and control over the
sync mechanism.