Bound vs. Unbound Text and Image Columns
When using server cursors, the SQL Server Native Client ODBC driver is optimized to not transmit the data for unbound text, ntext, or image columns at the time SQLFetch is performed. The text, ntext, or image data is not actually retrieved from the server until the application issues SQLGetData for the column.
Many applications can be written so that no text, ntext, or image data is displayed while a user is simply scrolling up and down in a cursor. When a user selects a row to get more detail, the application can then call SQLGetData to retrieve the text, ntext, or image data. This will prevent transmitting the text, ntext, or image data for any of the rows the user does not select, and can therefore prevent the transmission of very large amounts of data.