It looks like this won't affect the performance, but there is another annoying effect.

Excel (as many other applications) has a feature, where when you want to open a file, you can select from files lately opened with this program. When I run this workbook and process through ~1000 Excel workbooks in folder (without saving there anything), all those ~1000 forkbooks are listed as top of this selection list. I.e. any user who will work with this app, will get his/her latest opened workbooks list spammed with those.