I use MAMP Pro 4.0.6 on MACOS X El Capitan
I am noticing a strange behavior that I never noticed before: when I start MAMP, it creates a folder MAMP PRO\Assets folder inside /Users/(My user)/Documents
If I delete these folders, they are recreated on the next MAMP restart... As I said I never noticed that before and I don't know where this behavior comes from.
This is part of a feature introduced with MAMP 4 that allows you to manage project assets.
Within MAMP you can access the assets window under "Window" or ⌘-3. The window then allows you to add and remove assets. Any you add will be added to the new 'assets' directory in documents. Similarly, if you move something to that directory it will show up in the MAMP assets window.
I've yet to find a real use for this feature and, from what I can tell, Appsolute's only documentation of it is one line in their MAMP 4 launch blog post.