The ability to block would be far more selective than our current choices which is to either have a public tree or a private tree. It actually would open up a lot of information. Blocking is a far more specific action taken to prevent one individual or a few from seeing one or a few items whereas a private tree is blocking but on a far larger scale. On another site I blocked someone from a set of photos simply out of consideration. They had a family member pass away and had expressed distress over seeing photos of that family member (taken when he was alive). Other family members were comforted by the photos, wanted to share memories and wanted to see them. I blocked the one person and everyone was happy with that decision.