It could help in the long run to have the ability to toggle saving in excel activities, either per activity (preferred) or as a transaction-like scope.
There are use cases with legitimate reason to iterate over cells and modify something about them (latest being changing cell colors that are not a full range).
If there would be a boolean flag for those to not save immediately, it could save a lot of execution time. For compatibility reasons default should remain to save.
Major candidates for this addition would be WriteCell and SetRangeColor, but others could use it as well (AppendRange, WriteRange etc.).
As a secondary effect this would require an explicit ExcelSave activity, or other make-sure-its-saved mechanism.
While this may sound risky at first (users not saving their changes), with a proper default behaviour it would give more control and also allow effective manipulation of individual cells, which currently is a performance killer.