It might help strike up interesting conversation with fellow park guests while you are in the queues and it might earn you a hearty “Welcome Home!” from the DVC sales kiosk staff.
No disadvantages, beyond normal wear and tear on the backpack itself.
Pro- it carries things.
Con- you have to go through the bag check line.
We don;t have a DVC backpack. I have a shoulder bag that I received when we bought in eons ago, but I never take it into the parks. Prefer to go bagless when we can.
My wife and I both laughed at the tiny size of the backpack when we got it. We use it to hold the dog's toys, comb, etc... when they go to "camp" (boarding). It's really too small for us to use for anything else.
My question was what DVC backpack but someone already asked that question. LOL
I take as little as possible into the parks, I don't want to have to carry around or keep track of anything I don't really need. I learned this early on when I did carry a backpack to the parks. By the end of the day I was really sorry I had to lug that thing around.