When using the application "Drive File Steam" on Windows you will be able to "reflect" your Drive file tree on your Windows file system. When opening an excel file located inside a Powertools workspace from File Stream you  may encounter an error message when saving your excel file.

When your create a workspace on Powertools the "root folder" is created on Drive with the prefix [ w ] to help you identify your workspaces on the Drive user interface. The [ ] characters are authorized on Windows file system but it seems that excel is a bit more restrictive and forbid the use of [ ] in the file path. So when using File Stream to work on an excel file the path opened by excel looks like G:\My Drive\[ w ] - Project\excelfile.xlsx

As the [ ] in the folder name is just a "visual aid" you could totally rename the folder on Drive directly to remove those forbidden by excel character. Renaming the root folder of a workspace has no impact at all for Powertools as you may have already noticed.