Joe,
Yes, the Minors Possession Licence is very confusing. What it allows you to do is use a firearm under conditions that your parents or guardians negotiate during an interview with a firearms officer, that could include "direct supervision," which basically is the condition under which you can use a firearm without a Minors Licence. I'm guessing that if you've completed a firearms course, or otherwise had some instruction, a Minors Licence might allow you to use a firearm without "direct supervision" under certain conditions. But again that would have to be negotiated.
Since you cannot purchase or own a firearm with a Minors Licence, there really is no other value to it.
For more information on the licence, check out the
Firearms Centre web page on the subject.
Don