Foldermap.txt should only be needed when working with unmanaged data that you are adding to Insight where all or some of it was already managed in Insight.
An example is you export and send an assembly to an outside design service to be worked on and then they send it back to you and you need to put it back in Insight. The foldermap file is used to map the locations of the returned files to the locations where they reside in the Insight document libraries. It keeps Insight from trying to make new items and instead uses the existing and just replaces the file.
Ken Production: ST10 MP9, Testing: SE 2019 http://Grundey.blogspot.com