It makes the photos you are tagged in available to print, I know for me at least, that most of those photos are not mine. And when I go to print some, I am printing photos from multiple friends. You can imagine how painful it would be to go to multiple people (especially if they are not your best friends) and ask them to find specific photos from some point in time and send them to you, then you still have to go and print them. In the end the photo quality maybe better but it would take much longer than a few minutes, if you even receive all the photos you want.

The older photos on Facebook are pretty low res, but they do now have higher res ones available and are the proper res for 4x6 prints, I believe they have had this since adding the full screen image viewer.