What are some disadvantages of having exposed pins on a connector?
Well, if the cable supplies power at all times on exposed pins that are near each other, that probably will not end well. (Short circuits, etc if the host does not appropriately current limit). An additional ESD risk is also present.

Also, exposed pins are at a higher risk of damage -- bending, breaking-off, etc. If you don't notice, and try to make a damaged connector to its mating plug/receptacle, chances are that you'll damage the plug / receptacle as well.