I travel with mine. I find it easier to use for ID at the check point. Most checkers can understand the passport faster than a DL.

I also fold my boarding pass in half and slip it right into my passport. It's a perfect fit and means I am less likely to lose or destroy my boarding pass.

I started carrying it during the silly period of checking ID at every airplane door. I was afraid I would lose my license and be stuck at some airport trying to change planes.

Cromely.