At my house, I have a meter that I get a feed from. So I look at the graphs. From the graphs, you can learn about what is happening in the house. You know when someone is showering, left home for work (arrived home), doing laundry, went to bed/got up, used the microwave and so on. Some of that you could determine by watching the house, but that requires constant surveillance. A smart meter provides all this data with no effort and at mass scale. If I can glean that level of information just by glancing at the graphs, I'm sure someone better equipped could determine even finer grain details of what is going on in the house.