Synchronization batch size
As described below, if you have edited a large number of records while offline, you can then synchronize the edited data with the server-side database by sending data in batches. When the batch size is set to 0 then all of the edited, a.k.a 'dirty', rows are sent at once. The number next to 'Synchronization batch size' represents the number of edits to include in one batch of rows.
In a disconnected application a user might have been disconnected for quite some time. During this time they may have made a number of edits on their client-side device. When they get their connection back, the user might click a synchronize button in order to push their edits back to the server. However, because they made a large number of edits, it is quite likely that the server might take a while to actually process all of the changes that the user made. While the server is processing information the user/client will be waiting for a response and, if the server takes to long, the client-side device could time out before recieving said response. One way to avoid this problem is to send the user's edits to the server in batches, such that the user can get feedback as to what progress has been made.
For more on the subject watch this video or read the explanation below.