Whats the gotcha when trying to restrict access by setting the parent folder to READ ONLY and the files contained within to READ & WRITE?

Some applications require saving temporary files to the folders during the Save process. This happens in the background and cant be seen by the user, but if the folder the user is trying to save to is READ ONLY— although the file they are trying to save is READ & WRITE — the save may fail if the application tries to create backup or temporary files.

This is true of TextEdit.