If you set it to 1881 it'll show in deep blue where you're mostly likely to be from. With the actual family that I know where they were genuinely born going back to 1066 I would say that the map is a very good predictor of where the family was in the 13th century time period. If you can't trace your family back beyond the 16th century due to lost records, this is a pretty good substitute. You have to set it to 1881 though.
For example McCallum