What is the difference between giving BatchSize and not giving BatchSize for OracleBulkCopy

Can anybody give the performance & behavior difference between using BatchSize and without using BatchSize in OracleBulkCopy. Currently I don't specify BatchSize. My BatchSize may vary from 100 to 200000. Please suggest the best approach.

try
{
     var columnMapping =
         from table in orgTable.Columns.Cast<DataColumn>()
         select
             new OracleBulkCopyColumnMapping(table.ColumnName, table.ColumnName);
     using (var bulkcopy
         = new OracleBulkCopy(ConnectionString, OracleBulkCopyOptions.Default))
     {                    
         bulkcopy.DestinationTableName = GoldOrgTable;                                        
         foreach (var mapping in columnMapping)
             bulkcopy.ColumnMappings.Add(mapping);
         bulkcopy.BulkCopyTimeout = TimeOut.Value;
         bulkcopy.WriteToServer(orgTable);
         orgTable.Dispose();
     }
     return true;
}