PrincessShmoo nailed it.
Another PRO
You can be the first people in the building, excluding B2B'ers. It is a fun challenge for me to get on the first bus. This is really only good if you have a lowish PAT or concierge. But you can get all checked in and get a comfortable spot to sit and wait. Also you can check for upgrades too since they are first come first serve
We checked in 2 weeks ago online and since we had DCL transportation from MCO already booked we didn't even need to pick a PAT. Was told from others that recently had similar experience that we'd get a boarding number based on when we arrived at port (similar to the old days).
I'll report back on our experience with boarding number (this is our last cruise before platinum so it will be a fun final boarding card experience).