There are multiple ways to connect to SharePoint with Data Sync. Originally we used the legacy ASMX Web Services now we use the Client API and in the future we will create a new connector using the REST/Web API endpoints.
With Data Sync you can Read and Write List Items and Documents in Document Libraries. We are still bound by the limits of SharePoint so if you plan on more than 5000 items in a list ensure you configure indexed columns.
If you plan to have more than 5000 items in your List(s) it is a good idea to plan ahead and configure SharePoint Index Columns. You should index any columns that you might use to filter the list for example if you plan to use incremental sync against the list ensure that the key column is indexed on the SharePoint List.