“Old dough” is a term for the dough that was carefully saved just before shaping the bread. It was used to leaven the next batch of bread in the years and centuries when one couldn’t purchase yeast from a grocery store. Today people prefer to call it sourdough – though old dough and sourdough aren’t exactly the same: generally speaking, sourdough is more carefully “fed” and handled with loving care..
Currently the people most likely to keep a culture of wild yeasts in the refrigerator (that’s what “old dough,” or sourdough, actually is: a culture of wild yeasts) are those of us who love bread that has a lot of taste and different textures. Some of us prefer to use sourdough for health reasons. Others are just curious. Whatever the reason, having a wild yeast culture in the ‘fridge means one can make breads that aren’t normally available. It’s fun, it’s good for you, and it doesn’t cost much. What more can one ask from a hobby?