When importing transactions you can "adjust" bank data to clean the import by adding a code such as "Sponsor" to the description or "Dave Fields - 115" to reflect the invoice. Rules should be able to look for "Sponsor" or "Dave Fields" but still import the transaction details as it was on import to retain additional information such as invoice number, sponsor name.
I don't think the "Description set to" field should be there at all. Whatever transaction information is imported from the bank statement should be left as it is and no part of it deleted/changed due to creating a transaction rule which is supposed to make the program more efficient and user-friendly.