Not just old photographs
Practically all photographs can benefit from some retouching. Color correction, sharpening or blurring parts or the entire photo, all of these will generally improve even modern digital photographs.
This is a digital snapshot of a family heirloom, a cross-stitched tribute to those who served in World War I (note the date 1918 in the bottom center). The stitchwork is under glass, and it is mounted on a wall. This digital photo was taken in place, without touching or disturbing the heirloom, nor exposing it to hours of bright lights. Afterwards, with careful adjustment of the digital image, the colors of the stitching seem to almost glow. Look at the tips of the flagposts.
If you live in the western