When you upload a photo, you get prompted to identify individuals in the photo, and it tags their profile. This is a nice feaure because the photo then gets associated with other profiles.
However, I've got a pretty extended family tree, and have "invited" other members of my family to participate. Some of the ones that have "accepted" are flagged in such a way that I can no longer link their profile to a photo I've uploaded. I can understand that someone might want to lock their profile (or whatever), but in the case of a group photo (and I've got many), this means that the individual who has now taken over their own profile doesn't get to see the photo's I've uploaded. I've also got to go through an extra step to label the photo with the names of people in my tree, but who I can no longer "tag".