Well the plus side of Passbook is that unlike KeyRing and the individual apps, it is supposed to automatically pop up your loyalty card when you arrive to that location.
Until it's more widely used, I've turned off Location Services for Passbook to save a little bit of battery life.
I'm not a fan of all of my apps having access to my location. I'm also one of those people who go through the settings of both devices and apps and limit what they can do in regard to my information & location. Still, the feature in and of itself is very nice.
