I want to make this point one more time about scanning pictures at a high resolution. So here is a much more clear example of why you’d want to.
Here is a sample from a picture that was taken in 1906. The first initial scan was done at 150dpi. It was a ‘satisfactory’ job because it was a large group picture. However, when looking for the actual detail of any one particular person, that detail just was not there. Both of these pictures are actual size, I did not rescale them to fit this post.
1906 picture scanned at 150dpi
1906 picture scanned at 1200dpi
I rest my case.