It allows you to map folder structure to another one. It is intended for the cases when you can't change original folder structure or want to have alternative view(s) or just want to focus on particular task, feature or aspect or...
Extension doesn't provide UI for everything, so, editing config files sometimes is okay. It is located in root of solution: parallelFolders.json.
I already use the extension in my everyday job (to be precise the version of extension for VS Code). Usually real life projects are big and cluttered. What is even worse they often structured not according to business requirements. They often structured as hello world projects where files are grouped by file types (you know: Controllers, Views,...). The problem is that when the project grows this structure starts working against you. The bigger the project the bigger the part of time you spend on navigation in a mess. The most close proof of concept is well described in MSDN article: https://msdn.microsoft.com/en-us/magazine/mt763233.aspx?f=255&MSPPError=-2147217396 Being unable to restructure the projects in most cases, I have created this extension. It has proven itself as indispensable tool to stay focused only on things I need. There is actually quite a lot of other reasoning and I could go on and on about it for quite a long time (this was really a pain for many years). In particular reasons from the modern neuropsychology and a book "Algorythms we live by" but I keep it for next time.
It may be quite confusing at the beginning because what you see initially is just empty panel. So, it is easier to understand usage from the two minutes demo video: https://youtu.be/VQzgzhwMMw4. The video is for VS Code's version of extension but should suffice.