.
...
When a user requests an Excel document, you can first check to see if there is new data. If there is, you can generate a new report and save it to disk. You can then stream that file to the user. We have a KB article which describes how to stream a file to the user that was previously saved to the disk with ExcelWriter.
Apply Styles to
...
Columns and Rows, not
...
Cells
Every time Cell.Style is accessed, ExcelWriter instantiates a separate Style object. To reduce file size bloating, we recommend using Global styles and setting styles on groups of cells. For details, see Effective Use of Styles
Applying a style to an Area also creates style objects for each individual cell in the Area. However, if you apply a style to a column or row, there will be only one formatting record for the entire column or row, which is much more efficient. Use ColumnProperties.Style or RowProperties.Style
Use InsertRows instead of InsertRow
...