When that box is unchecked, Toad runs the query again (separately from the cursor that is tied to the grid).
In the "new" query, after a row is processed and sent to Excel, Toad releases the row from memory.
When that box IS checked, then we use the cursor that is tied to the grid. Grids need to be able to scroll forward and backwards, so we can't release the rows from memory after they are exported.
There are really only 2 cases where you should leave the box checked.
- Your query took a long time to run AND it does not return very many rows, OR.....
- You don't want to risk getting a different result by running the query again (like if another session changes the data after your initial SELECT)