I understand that VLC player is designed to play from a "server", but there are many who like to use VLC as a standard desktop media player as well, due to it's stability and support for a huge range of codecs.
VLC (by default) opens a separate instance of itself for every new media file. My issue with this, and hopefully a developer can consider this request from a useability perspective, is that the "run only one instance" and "queue new files" checkboxes are hidden in the default preferences view.
I think it should not be in the "advanced" section of options, because normal users expect a player to open one instance, and queue new files (not open multiple instances). The option should be in plain sight, not hidden in plain view.
As of now, to change the setting so that VLC player only runs one instance, you must choose Settings -> Preferences -> Check "advanced options" box in the bottom left corner (easy to miss that checkbox btw) -> Advanced -> Other. Now, you can check the box for "allow only one running instance" and "enqueue items to playlist".
For such a simple, and basic, option - it is hidden under too many layers of complexity. Please consider this usability request.