I can't say I fully understand it yet, but I used it during the making of all the
17 Technic Constraction parts I made recently.
Here's how I think it might be intended.
LPDE scans, at start up, two libraries. Official and Unofficial Part, including all subfiles and primitives.
The creation of a Project adds a third library, to scan at start up, containing all the new files you make in a correct library like structure. It made all the new subfiles I made easy to access. Just right click on the file you want to edit, an choose 'view in 3d/text editor'.
I don't see the point in making a new project, including a
complete library structure, everytime I wan't to make/clean a part. I keep all my new parts in separate folders, and move them to the unofficial folder after they are uploaded to the PT. Handling my files should be as easy as in windows explorer. LDPE can't find a correctly placed subfile in a folder (named 's' in windows explorer)
unless you first create a project. It seems to need to know were to look for it.
I still find the editing of a part-files subfile structure much easier in LDDP, using the move, or rotate, in x,y,z-direction-buttons. LDDP rotate everyting around world origin.
The obstacle is the Manipulator placement meny. I want the setting of the rotation center in LDPE to become better. I ended up using a helper file to set the manipulator were I wanted it to be. But I'm beginning to like the Manipulator.